The mandrel headstock may be compared with the larger drawing which follows, to better see the form of the mandrel and its bearings, &c. The large drawing of the mandrel, with the collars and a portion of the headstock casting in section, shows all the details of these parts. The mandrel drawn immediately below is shown in section, the drawing-in spindle being removed. All dimensions can be taken from these drawings, which are not like the "Kearney" headstock in every particular. AMATEUR WORK. By J. LUKIN. rounds off angles that ought to remain sharp, files out hollows and chamfers intended to be ornamental, but which are, I am place. It WHY is it that there is ever a something instead, decidedly detrimental. It is entirely in the term "amateur" in relation to an amateurish practice to get work approxiwork which implies imperfection. The word mately correct, and to "let it go at that." itself, in the sense in which it is now most But if a flat is required, make a flat, and if commonly used, is not of very ancient date, you cannot do so go to work again, and but has mainly become prominent during again, and yet again, till you can. one kind of the last half-century. Its meaning, it need not speaking specially of not be said, is "a lover"-not by any material, and it matters not whether the means a modern creation, for it came in with work is of wood or of metal, whether plane Time, and will last indefinitely beyond it. and chisel are needed, or file; but in no case Now a lover is generally believed to be so is a flat surface a rounded one, concave or The bed, headstocks, standard, &c., can be enamoured of a certain object that he will convex, and therefore these forms canmade of cast iron, or bronze if preferred. spend any amount of time, care, or trouble not be allowed to take its When finished they may be nickel-plated, upon it, whether that object is animate or is not, indeed, concavity which is so which makes a very handsome finish. The inanimate. But all who have a hobby may to be feared, but convexity, or alternamandrel, drawing-in spindle, tailstock barrel, be called amateurs in respect to that hobby. tion of the two. A flat surface bounded traversing screw, are steel; and these, as The President of the Royal Academy is as by straight lines becomes a startingwell as all other steel parts, should be of much an amateur a lover of his art as point of measurement in various directions; good quality cast steel. The pulley, and the struggling schoolgirl making her early but a rounded or uneven surface entirely hand-wheel on drawing-in spindle should be efforts in water-colour drawing, although fails to do this. You cannot lay a ruler vulcanite or hard wood. The sleeve for the in one case the result may be a picture need-upon it with certainty of contact, and when, pulley and the centre-piece for the hand-ing four or five figures to purchase it, and as is generally needed, the piece has to be wheel may be of bronze. The caps over the the other a little unlovely paper-staining. drilled, mortised, or otherwise worked upon, collars may be of bronze or brass. But the president himself was also a paper-it throws out of correctness all pieces fitted It will be noticed that oil channels are pro-stainer, for it is only in a limited sense that to it. Why does the amateur's table insist vided in the collars to convey the lubricant all over the bearing. The oil is applied by removing the outside caps and pouring it in the holes shown in the tops of the collars, just against the headstock casting. The collars are made long, so as to give bearings for the caps, but it will be noticed that they are enlarged at their inner ends, and therefore the mandrel does not bear the entire length of the collars. Also the bore in the headstock casting is enlarged in the middle, and the collars fit at the ends of the bore. This is a simple and efficient plan for insuring against a tight fit near the middle of the bore, which may result in a collar being heid near its middle, and yet with its ends free to shake sideways. we can say of an artist "Nascitur, non fit," and upon standing on three legs instead of four? under certain circumstances that same pre- Why is that wonderfully designed towelsident would have remained an amateur. horse awry?-simply because the wood was How happens it that he did not so remain? not truly surfaced, and therefore it was inSimply because he loved art so well that he accurately squared, and consequently tho gave up all else to pursue it. Pencil, chalk, tenons and mortises were cut at indefinite or brush was ever in his hand under the angles, all probably different. Ask a comguidance of able and experienced teachers petent workman to square up an iron bar until he became a master in the interpreta-say in., and 4in. or 5in. in length, such as tion of nature's handiwork. a a versus would be needed for the shank of an eccentric To an eye capable of appreciating subtle cutter-frame or drill, and set it side by side qualities of form and colour, there is no with a similar piece done by the average hesitation in deciding upon the genuineness of amateur. The eye at once recognises the the work of a trained artist. There is difference decision hesitation, decision in every stroke of the brush, and in definite form versus uncertainty. Probably every tint and gradation of colour, which the amateur's work is most polished, for the the hesitating hand of the amateur artist fails workman has paid little attention to that The index-peg, shown through the left- to attain. This decision is not in itself a kind of finish. It can be added ultimately hand upright of the headstock, is made of gift: it is the result of downright hard, if required; but his entire energies have been steel, well fitted to the hole in casting, and ceaseless, painstaking work, by which only directed to the production of an accurately having a chequered head by which it can the eye is trained to perceive, and the hand faced and accurately squared bit of iron be held with the thumb and finger. It is to execute. This work it is next to impos-of given length, and there it is shown with the peg in a hole, but it is with-sible to carry out if art is only taken up as The fundamental principle of all real work drawn when the mandrel is to be revolved. amusement, while some exacting business or is accuracy, whether such work be artistic, The dividing-plate has but one circle of holes, trade demands the chief hours of the work- mechanical, or (facile princeps) matheusually containing sixty. ing day. There is not sufficient time avail-matical. A very slight disturbance of the The slide-rest for this lathe is next shown, able. The hand is too often fatigued by balance of the forces of nature would result top, base, side, and front views are given, manual labour before the pencil or brush in the shipwreck of innumerable worlds, also a view of the base; all are drawn to can be assumed. The attention is divided and every teacher who knows his work the same scale. The lower or long slide is between the bread-winning pursuit and the will insist upon accuracy in that of his 3in. long, and the upper or short saddle is art, which of sheer necessity becomes a pupils. If he fails in this, his pupils will 2gin. long. recreation, and not the work of life. The never rise above the mediocrity of amateurs; necessary result is that the would-be artist nor is he himself entitled to any higher title. falls into the position of an amateur, and I have been at some pains to discover why that distressing title is stamped only too it is that amateur work is not more accurate, evidently upon his work. There is also and I have found that one common reason is another amateur artist who ought to do that the tools which he uses are very rarely better, because he has private means and in good condition. They are either blunt, or ample leisure; but here again amusement endeavour. and recreation take the place of serious Generally speaking, the dry mechanical work which underlies skill is shirked, elementary exercises are slurred over as unnecessary, and what little of nature the untrained eye discovers, the hand fails to execute. The base of the rest fits on the shoe shown under the T-rest in the complete lathe. The three screw heads shown in the base hold the lower, or main, slide to a tapering disc fitted in the base and free to swivel round somewhat stiffly, and which may be fixed by the pinching-screw shown in the front view. The crank handle on the traversing screw of the long slide fits both ends, and may be used on either according, as the main slide is placed parallel to the lathe centres or at right angles to them. their working parts inaccurately set. Take, for instance, the plane. Its name suggests what it ought to be-viz., a plain, flat surface, capable of reproducing itself upon the work in hand. Supposing the sole of a plane to be truly level (which it often is not), the cutting edge needs to be a right line The saddle of the main slide is traversed by almost coincident with it; the amount of means of the nut fastened to the saddle by We may gather from art education and variation from such coincidence representing two screws. This nut passes along a groove its exacting requirements, the difference in the thickness of shaving to be detached from cut in the edge of the lower slide. The top all cases between the work of amateurs and the work by its traverse over its surface. slide and its saddle are shown in each view. professionals. And there is one special This cannot be the case if the plane-iron The tool-holder is a peculiar arrangement; a need which is suggested by what has been presents a curved ог uneven edge, tube bored through eccentrically, and written above, and which applies to mechani or if one part projects more than the capable of being rotated in the pinching cal handiwork quite as much as it does to other. The latter fault accounts for device, affords a certain amount of adjust that of the Academician, viz., decision of the fact that, although a piece of ment for height. An adjustable ring, shown form and accurate definition of line. This I wood has been squared up with the aid in section in the side view, is also provided to have attempted to show can only be attained of what is known as a shooting-board, give further vertical adjustment. Those by diligent and painstaking elementary the result is inaccurate. In shooting a mitre, fairly well acquainted with this class of work work, careful and constant handling of the for instance, the amateur often finds that the will find these drawings of the " Kearney' "tools-whether pencil, brush, chisel, or file- pieces do not fit closely together: the bevel is slide-rest sufficient to make its construction by which the work is to be done. Now, not at right angles with the plane back of apparent. Perhaps larger drawings of each precision of form is just that point which the the strip of moulding; and then comes the part shown by itself would be welcomed by ordinary amateur is so prone to neglect. He hazardous process of touching up the surdoes not rightly square up his work; he faces with a chisel, which usually increases some would-be constructors. ENGLISH MECHANIC AND WORLD OF SCIENCE: No. 1376. the error. But the whole difficulty has arisen from the cause stated above-the projection of one part of the plane-iron-because its edge was not ground precisely at right angles to its sides, or because it has not been accurately placed in its wooden bed. Sometimes, but rarely, the woodwork of the plane is not of accurately square section. This would not signify in the work of planing a level surface; but when the plane is laid upon its side upon the shooting-board, it cannot possibly be relied upon to square up the work. After a plane-iron is ground and set on the oilstone, it should, when returned to its place, present to an eye directed along the sole of the plane, a thin, bright, well-defined line truly parallel with the surface of the wood. I am speaking, of course, of a trying plane, or one used with a shooting-board, and also a smoothing or finishing plane. Jack-plane irons are purposely ground with a slightly curved edge; but these are only for rough work to be finished to a level surface by the trying plane. like joint cannot result, because the tenon JOHNSON'S ROTARY ENGINE. THE illustration shows in cross section an im- of angles to the axes of the vane and valve cylinders It is in the matter of tool-sharpening that amateur work suffers so terribly in comparison with that of professional workmen. Amateurs need practical instruction in this particular quite as much as they need it in the subsequent manipulation, and I have merely taken a plane as a primary example, because perfect surfaces in wood are unattainable without them, and if they are blunt or their edges misshapen, these defects will necessarily reappear upon the work. But another tool to which these remarks apply is the saw, for to cut accurately close to a pencil or scribed line, yet without defacing it, is a matter of impossibility if the saw is blunt or badly set or buckled. Many an amateur has never considered the true nature of saw-edges. The teeth do not stand like a series of minute chisels, one in front or recesses, and also the relative time the periof the other, but are more like what two the periphery of the cylindrical valve as the vanes phery of the vane cylinder is out of contact with chisels would be tied face to face with their are passing the openings therein. The improvebevelled faces inwards, forming two knife- ments consist in driving the cylindrical valve at edges a little distance apart. are practically those of two knife-edges, the and in modifying the form of the recesses or The two cuts a greater surface speed than the vane cylinder, intermediate wood being ground into saw-openings in the valve to allow of this increased dust by the action of the edges of the teeth speed. between the knife-edge portions. Hence a well-set saw will cut a line almost as evenly and cleanly as if it were actually done by a knife-edge; and it is of no importance on which side of the saw the guide - line may be. A carpenter takes exceeding care of his tools, and never of using his sharpest saws dreams but best work. upon any For rough outdoor jobs he uses a tool which is specially retained for that kind of work. I never recommend an amateur to trust to his own saw-setting, unless he has learned the art from a practical hand. Saw-filing is not easy to do in a workmanlike manner, and saw-setting is still more difficult; and 6d. will always obtain the services of a skilled carpenter, who will set the teeth wide or narrow, according to the stuff it is intended to operate. But in all workmanlike work, as distinguished from amateur, saw cuts are made accurately to line at once and decisively, leaving, not smooth, but clean-cut, even surfaces. tool, and I have done: the chisel. Here, One more ain, compare that of a carpenter with one rpened by an amateur: tento one the bevel he latter is rounded instead of flat, from g ground in a hurry, and therefore carey; and as in the defective plane-iron tear. cannot see the thin, straight, bright line of produced on the carpenter's chisel by portions of the valve and vane cylinders are By this method of construction the cylindrical oilstone. This little supplementary almost continuously in vel, straight and even, is always seen in a exception of the comparatively slight break as contact, with eenly-sharpened tool. Note the result of the vanes pass, and as it is far less costly to preach in cutting a mortise. The badly- pare such cylindrical faces to work accurately sharpened one, at the blow of the mallet, together without leaking, and maintain them in breaks and bruises the fibres of the wood, working order, the initial cost of this class of tead of cutting them clean through, and effectiveness is not nearly so dependent upon the machinery is considerably reduced, and the ally the hole is rather as if it were accuracy of the form of the valve openings or out by some malicious rodent. No recesses, so that better results are obtained mortise is flat, and a workman- generally. AUG. 7, 1891. HOW TO CONSTRUCT A BE By W. GILLETT. 26.-Speed-Reducing Wheels. ETWEEN the electro-motor and the phonoand has fastened on it a small wheel fin. in graph shaft there are two pairs of wheels. The wheel next to the motor is 2in. in diameter, This pair of wheels are shown at Fig. 35. The diameter, both these wheels having V grooves. I will first describe, consists of a 33in. length second counter-shaft, the construction of which and carrying at one end a brass wheel 3in. of in. steel rod, carefully centred at both ends, in. diameter. The shaft and wheels are shown in diameter, and at the other end a small wheel of plan and elevation in Fig. 28. The large wheel shaft with the exception of the boss, while the a may be an exact pattern of the one on main small wheel may be turned down from fin. brass rod, leaving a small boss, as seen at b, to give the surface in contact with the solder greater length when the wheel is sweated in place. A V groove should be cut on each wheel, the bottom of the grooves being about 3§in. and in. diameters on the large and small wheels respectively. Both wheels can be sweated on the shaft before turning, and may with advantage have a small pin running through the boss and shaft. The distance of the V grooves apart will be about 3in. 27.-Counter-shaft Supports. The shaft described above is mounted between two steel centres similar to the main shaft. The bottom one, Fig. 29, a, is a pointed steel screw in. diameter, and about in. long from point to shoulder, being of course well hardened. A piece of brass of the size of b has slots in. wide and in. long, cut at each end as shown, the brass being in. thick. One side of this piece is surfaced off, and a central hole is tapped to take the screw centre just mentioned, which is above the surface side. screwed firmly home with the point projecting of the shape and size of c, are drilled with three brass, the same thickness as the above piece, and Two smaller holes, the central hole being drilled to allow pieces of a in. thread to be cut therein, the remaining screws, by which they are fastened to the wood holes being counter-sunk to take brass wood base. Two steel pins in. long and in. diavented from twisting round by a small pin which screwed into the central hole of e and are premeter, having a good thread cut on them, are through the walls of the hole and threaded pin This hole is seen at d. is inserted in a hole drilled for the purpose small diameter, about 20 B. W.G., and of steel. A hexagonal brass nut, e, is made to screw on the The pin should be of pin, and a thin washer, f, of in. diameter is slipped on the pin, against which the nut may be section at g, which also shows the section of the screwed. The pin, nut, and washer is shown in bottom piece is, of course, the elevation of c. slotted piece held firmly down in place. The is in the centre of the slot in the hardened base-board in such a manner that when the pin The pieces of brass c are screwed down to the formed by four of the pillars at the left-hand side screw centre shall come in the centre of the square of the machine. the full size of the vane cylinder from the exThe diameter of the valve cylinder is equal to tremity of one vane to the other, and their shafts E and F are geared together by wheels of equal considerably larger diameter than the cylindrical size; consequently, the valve cylinder being of of the former is proportionately greater. This portions of the vane cylinder, the surface speed increased speed enables the valve opening e e to be reduced in width, and also greatly reduces the time the cylindrical portions of the valve and piece, a, Fig. 30, mounted on two pillars, b. A vane cylinders are not in contact with each other. circular hole rather over in. in diameter is cut The top of the shaft is supported by a bridge The extremities of the vanes i pass into and in the brass bed-plate exactly over the lower leave the openings ee approximately at the centre. This hole is to allow the small wheel on shape that the vanes do not meet the sides of the this hole two smaller ones are drilled to take the centre, as shown, and the openings are of such a counter-shaft to pass through. openings until the cylindrical portions of the valve stems of the small pillars. On each side of The vanes pass from contact with the sides of the by which they are held down to the bed-plate. and vane cylinders are on the point of separating. a in. thread, and take a small nut and washer, openings as the cylindrical portions again meet, This is shown in section at Fig. 30 at e e. The The stems have so as to avoid unnecessary friction and wear-and-diameter joining these two holes in the bedwide, being about in. thick. plate is at right angles to the main shaft. The bridge piece a is 13in. long and in. takes the top steel centre, which is fitted with a milled-head and lock-nut seen at d, the screw this piece a hole for a in. screw is drilled. This In the centre of itself being about in. long. piece is shown at Fig. 33, and an elevation of the piece with front pillar removed is seen in Fig. A plan of this wheels mounted in position. 32, which also shows the side view of the bridge piece, part of the instru counter-shaft and Fig. 34 gives a the • All rights reserved. trained?" ment being removed. The pillars can be securely "What is fitting?" 28.-Guide Wheels. "How is the fitter has been that of a general shop, and not that of a special shop or department. Fitting, in its broadest sense, includes the I have been rather interested lately in the union of the various portions of which a mechanism letters that have been appearing in a contemis composed. It embraces more or less of the porary on "How to become an Engineer." It preliminary preparation of parts, as well as their seems pitiable that so many young men with subsequent union. It also embraces the repair energy, book, and college learning should spend and reconstruction of all classes of engineer's so many fruitless years in the hope of gaining work. It includes the smallest and most delicate some appointment worth perhaps no more than machines and models, and the largest and most from £2 to £4 a week. To think that after seven powerful engines, cranes, and pumps, and all the or eight or ten years of preparation young men thousand and one forms in which mechanism should be waiting in eager expectation-waiting occurs. It embraces the manipulation of all the with heart-sickening deferred hope for an common metals and alloys, together with a prac-"appointment," struggling among scores or tical knowledge of their properties and special hundreds of applicants for their one poor chance uses. A rough and ready knowledge of approxi- of engagement! To such I would say: "Don't mate strengths of ropes, chains, and beams; a bother about an appointment," but qualify your good idea of the best methods of slinging and selves to get a "job" as a working fitter. You hoisting heavy castings, forgings, and parts of can always get bread-and-cheese at that, if you machinery; and good working ideas of the give as much energy to it as you give to the nature, and properties, and behaviour of water, technical side of the business." I say, and say steam, gas, and air. The practice of fitting pre- it deliberately, that a good fitter need never be The wheels are supported by a short pillar, c, supposes good physical health, able to stand the out of work for a single week. The employers which can be turned from in. brass rod. One-extremes of outdoor winter temperature, the want him quite as much as he needs them. I half of the side nearest the top is cut away, to might say much the same of any other branch of allow the wheel space to revolve; and care engineering; but I am specially writing of should be taken in drilling the hole for screw fitting. not to run the drill right through the metal, as this would not look well. These pillars are fastened to the bed-plate by means of a screw from beneath. These are to change the direction of the band from the horizontal to the vertical position, and vice versa. The wheels themselves (a, Fig. 31) can be turned from in. brass rod, and are in. wide. The central hole in them is in. diameter, to run on steel pins, b, with hexagonal heads. On each side of the wheel a small boss is left to prevent undue friction, and the circumference of the wheel is, of course, turned V-shape. The position of these wheels can be seen by inspection of Figs. 32, 33, and 34. 29.-Small Intermediate Wheels. These come next to the motor, and are fastoned together without a shaft, as seen at a, Fig. 35. They can, of course, be cast in one piece, or the large one a cast wheel, and the small one turned down from rod, as was mentioned in the case of the small wheel on the counter-shaft. Both the wheels have V grooves in them, the large wheel being about 13in. diameter at the bottom of the groove, and the small wheel in. diameter. The central hole through both wheels is in. diameter, and fits on a support, b, fixed in the wood base. This support should be made from steel, having a good shoulder, f, against which the wheel may bear, and at the top a thread, g, on which is fitted a milled headed nut, e, to keep the wheel from being lifted up. The lower part of the stem has also a thread cut on it, h, on which a hexagonal nut, d, and washer fit. The length of the part depends, of course, on the length of boss of wheels, and, including the short boss on top of small wheel, will be about in. The wheel, of course, turns on b, which is a fixed support. Two pieces of brass fin. thick are cut and slotted like e. These are sunk into the top and bottom of the wood base, so that their surfaces shall be flush with the top and bottom of the wood, and in such a position that the centre of the slot shall coincide with the line joining the two central pillars, the length of slot being at right angles to this line, and, of course, in the centre of the board. An elevation of these wheels mounted on their support fixed in the base is shown in Fig. 32, at A. The slots, both in the mountings of this wheel and that of the counter-shaft, are intended to admit of the tightening of the driving-bands. Fig. 36 is a plan of the bed-plate of electromotor, and will be referred to in the next article. It is made from in. brass, the distance between the slots being the same as in b, Fig. 29; in fact, it is a facsimile of that piece, with the addition of two ears or projections on each side, in the centre of which holes are tapped with in. threads. FITTING.-I. "E NGINE-FITTING" is the usual term by which this branch of engineering is denoted. I prefer, however, to make use of the title above because the term "engine" fitting is of too special a character. It might convey the impression that fitters have to do only or chiefly with the construction of engines-a too entirely narrow assumption. The range of their tasks is as wide as the general practice of engineering itself, and although there are numbers of men who are trained in, or who fall into special grooves of work, the general practice, and not special exceptions of the trade, must be considered in the articles to follow. In this introductory paper I shall only endeavour to give an answer to two questions: Now, I cannot teach fitters' work. No written articles can accomplish that. But what aid can be afforded by written description I hope to give. Having been among fitters and fitter's work throughout the whole of my working life, I propose to jot down those matters which are to my mind of the most fundamental, elementary, and important character. And I shall suppose my readers for the most part to consist of apprentices, and of those skilful amateurs who have lacked the set training of the shops, but who constitute so large a section of our readers. scorching heat of summer, and the close atmo- an evil How are fitters trained?-usually by spending After such an apprenticeship, a lad can become As regards the prospects of the trade:-The average of fitters' wages is about the same as that of the other branches of engineering. According to district, they will range from 28s. or 308. to £2. But a fitter has, I think, better chances in life on the whole than others. A large proportion of the men work by the piece, and so increase their earnings. They are in frequent demand on foreign stations and railways and public works, where they secure high wages, that, if husbanded for a few years, are sufficient to render them independent for life. Most of the works managers I have known have been fitters. As trades go, therefore, fitting is one of the best-at least, for the man whose training IN J. H. GEOLOGY FOR STUDENTS. University College, London. mentioned at the end of Chapter XI. Thus far we have defined Geology, con. sidered some of the most important terms used in the science, and studied the most important of the geological agents. Now that these matters of general moment have been dealt with, we are in a position to deal with matters of detail. We can pass to the study of the rocks that make up the crust of the earth, and to their arrangement in a series of successive formations. And first, the ROCKS. 66 A rock has already been defined as a constituent of the crust of the earth. We have now to see what are the different kinds of rocks, and to attempt to group or classify them. In any such attempt at classification, whether it is of rocks or of plants, or of animals, the student must always bear in mind that all classification is artificial, and is not natural. Groupings and definitions of the objects of Nature are very useful to the student, for mere purposes of remembrance. But the usefulness is apt to become a danger, unless the student keeps constantly in mind the fact that these divisions and classifications are of man's making, not of Nature's. That which was written in my Botany for Students" may with advantage be repeated here. "Classification is the arranging of [minerals or] plants or animals in certain groups, so that in our artificial tables of classification similar [minerals, similar] plants and similar animals may be found side by side. Such tables and such placing of [non-living or] living things in kingdoms, orders, species, and so forth, are artificial, in this sense. Strictly speaking, no such groups or groupings exist in nature. But, for convenience' sake, we group the bodies that we see around us into the mineral, the vegetable, the animal kingdoms,' and into subdivisions of these. No such divisions actually occur in the great world of things. The divisions are pure, but convenient, conventions." Rocks are made up of one or more minerals. FIG. 33. The well-known rock, granite, e.g., is made up of three minerals, quartz, felspar, and mica. And minerals are made up of one or more chemical substances. Quartz, e.g., is made up of silicon dioxide or silica (SiO2). Felspar and mica are salts of certain metals, silicates, in fact, of some or all of the following: potassium or sodium, aluminium, magnesium. And these chemical substances are made up of one or more chemical elements. Silicon dioxide, e.g., is made up of the two chemical elements, silicon (Si) and oxygen (O). To use an illustration that must not, however, be strained too far, rocks consist of minerals, as sentences consist of words. Minerals consist of chemical substances, as words consist of syllables. These chemical substances consist of elements, as syllables consist of letters. And just as, occasionally, a sentence may consist of a single word, so a rock may consist of a single mineral. So, also, as a word may be a monosyllable, a mineral may consist of only one chemical substance; and as a syllable may be of one letter alone, the chemical substance may consist only of one chemical element. Graphite or plumbago, the blacklead of pencils, is a case in point. Graphite is a rock of one mineral, of one chemical substance, of one chemical element-carbon (C). From that which has been said, it is clear that any study and account of the rocks that make up the crust of the earth involve a certain amount of chemical detail. Indeed, the student of geology ought, strictly speaking, to be a student of chemistry first, just as the student of chemistry should have mastered the elements of mechanics, and the student of mechanics, in his turn, should have mastered geometry and algebra. As, unfortunately, this ideal succession of study is rarely realised in individual cases, and as many of us become interested in and begin the study of geology without any preliminary chemical training, a few notes are now given which, it is hoped, may make the study of rocks and minerals more easy and more complete. NON-METALS: the geologist, the latter ending is the only one of importance. Of the three elements entering into these ternary compounds, one is almost always oxygen. CaCO,, e.g., is the symbol of calcium carbonate (p.352); CaSO, is that of calcium sulphate; K,SiO, is that of potassium silicate. With these preliminary notes, and with the constant giving of the true chemical name of the rock constituents that may be mentioned, and the equally constant use of the chemical symbols of all chemical substances mentioned, I think the student will be able to master the necessary chemistry of the rocks. The best plan will be to give a brief account of OXYGEN (0), SILICON (Si), the chief rock-forming minerals, and then to CARBON (C), sulphur (S), hydrogen (H), chlorine give a brief account of the chief rocks and (Cl), phosphorus (P), fluorine (F). attempt to classify them. But before doing this, According to Prof. Archibald Geikie, 99 per let me, once again, insist upon the absolute cent. of the rocks that make up the crust of the necessity of this part of the work being conearth consists of these 16 elements: gold (Au, ducted hand-in-hand with practical work. If aurum), silver (Ag, argentum), copper (Cu, the student is now going to read about minerals cuprum), tin (Sn, stannum), lead (Pb, plumbum), and rocks, without seeing, touching, handling, and other even rarer metals making up the odd smelling, and tasting them, his labour will be, 1 per cent. Further, 97 out of the 99 per cent. in the main, labour in vain. One of two things, is furnished by the six metals and the three non-at least, he must do, and, if possible, both of metals whose names in the above list are in them. (1) Have his own collection of the more capital letters. ordinary and frequent minerals and rocks. (2) Get access to a complete geological collection. When he is reading of quartz, or granite, or limestone, he must see that of which he reads. This premised and insisted upon as an absolute condition of real work, let us next see what are the most important minerals. A chemical compound is a substance resulting from the chemical union of two or more elements with a change of properties-that is, the chemical compound has properties that are not those of its constituents. Ice, water, and steam, e.g., are all one and the same chemical compound of the two elements, hydrogen and oxygen, in the proportion of two atoms of hydrogen to one atom of oxygen. H2O is the symbol for this compound-hydrogen oxide. In any one of its three forms-the solid ice, the liquid water, the gas steam-hydrogen oxide has properties quite other than those of either hydrogen or oxygen. On the other hand, a mixture is the result of the mere mechanical commingling, without any chemical union, of two or more bodies, with FIG. 34. Minerals. They may be grouped as elements, "ides" (of two elements) and "ates" (of three or more elements). (1) Elements.-Only three of the chemical elements or simple bodies enter "native" (i.e., uncombined) into the composition of rocks. They are carbon (C) in the form of graphite, already mentioned; sulphur (S), and iron (Fe). (2) "Ides." The commonest of these compounds among the minerals are the oxides. Of these, silicon dioxide (SiO2) is the most common. It appears as quartz, its purest, crystalline form, flint, opal. Then follow the iron oxides, some of which are valuable ores. Red hæmatite is a compound of formula Fe,0,. Brown hæmatite is a compound of formula 2Fe,O,, 3H,O. dpa (haima), blood. Magnetite, the magnetic ore of iron, or the lodestone, has formula Fe,O Still amongst the "ides rank calcium fluoride (CaF), fluor spar, sodium chloride (NaCl), common or rock salt, and the many metallic sulphides that are in several cases the As far as we know, our earth, and, for the chief ores of the particular metal they contain. matter of that, the planets of the solar system Galena, or lead sulphide, has been mentioned; generally, are made up of some 68 chemical cinnabar, or mercury sulphide (HgS), and blende elements or simple bodies, none of which has out any change of properties-that is, a or zinc sulphide (ZnS) are two other examples. thus far been decomposed into yet simpler mechanical mixture has properties that are those (3) "Ates."-First amongst these rank the bodies. Each of these elements is, for brevity's of its constituents, and could be predicated from silicates, i.e.,compounds of silicon and oxygen with sake, represented by a symbol, consisting of one those of its constituents. The air, already one or more metals. The various kinds of felspar, letter, or in some cases of two letters. The considered in an earlier chapter, is ae.g., are silicates of potassium (K) or sodium. student of geology is strongly advised to get into mechanical mixture of certain elements (nitrogen (Na) and aluminium (Al). The various kinds of the habit of using these symbols for the elements. and oxygen) and certain compounds (carbon micas are silicates of potassium or sodium and If no other advantage follows, that of saving of dioxide, hydrogen oxide, &c.). Most of the magnesium. time does. rocks entering into the composition of the crust The sixty-eight elements are artificially of the earth are mechanical mixtures of two or separated into metals and non-metals. The more minerals. Granite, the example given metals, iron, gold, e.g., some fifty-three in number, are generally solid, heavy, bright, bad conductors of heat and electricity, and can be drawn out into wire, and hammered out into thin plates (malleable). Duco, I lead; malleus, a hammer: The fifteen non-metals, oxygen, hydrogen, e.g., are generally gases or liquids, light, without lustre, bad conductors of heat and electricity, not ductile, not malleable. above, is a mixture of quartz, felspar, and mica, The carbonates come next, and are compounds of carbon and oxygen with one or more metals. Calcium carbonate (CaCO3) in its various forms of Iceland spar, limestone, marble; and dolomite, a carbonate of calcium and magnesium, named after the French geologist Dolomieu, examples. are Finally, the sulphates are compounds of sulphur and oxygen with one or more metals, The most frequent examples are calciun sulphate (CaSO) in its forms of gypsum and alabaster; alum, a sulphate of potassium (K) and aluminium (Al), and barium sulphate (BaSO). In our next chapter we shall show how these, the most important minerals, and others of less importance and frequency are blended mechanically together and form rocks. Let us turn and confine our attention now to chemical compounds and their naming, Obviously, the simplest chemical compound must How artificial even such a broad division as consist of two elements and of one atom of each this is may be seen from the facts that (1) every element. An example is calcium oxide or lime, one of the above qualifications of a metal or of CaO, p. 352. Carbon dioxide (CO1) and silicon a non-metal fails in particular cases; (2) there dioxide (SiO2) are as simple in that they only are three of the non-metals that are often classed contain two elements; but they are thus much with metals, and are certainly transition forms more complex that each of them contains two between the two groups; (3) hydrogen, apparently atoms of one of the elements-oxygen, to wit. the most non-metallic of non-metals, is probably A compound of two elements only, no matter & metal in its most gaseous form. what is the number of atoms of either of the elements, is always named after the manner of the two examples just given. The ending "ide" is invariably employed. Thus NaCl represents sodium chloride, rock salt, and new students' microscope, devised by Mr. common table salt; CaF, represents calcium T. T. Johnson, so favourably commented on at fluoride or fluor spar; FeS,, iron disulphide or the meeting of the Royal Microscopical Society iron pyrites; PbS, lead sulphide, the ore galena. (see p. 379). The microscope is manufactured A compound of three elements has for its name- by W. Johnson and Sons, of Tottenham Courtending not "ide," but "ite" or "ate." For road, and is especially designed for high power Fortunately for the geologist, only some 16 of the 68 elements enter to any extent into the formation of the rocks of the crust of the earth. They are: METALS: ALUMINIUM (Al), CALCIUM (Ca), MAGNESIUM (Mg), POTASSIUM (K for kalium, another name for potassium), SODIUM (Na, for natrium, another name for sodium), IKON (Fe, fetrum), manganese (Mn), barium (Ba). JOHNSON AND SONS IMPROVED IN N the engraving annexed we illustrate the 2 |