With an Alpha Laval separator separation will be complete at any temperature from 100° upwards, but generally it has been found that the cream will more readily separate from the milk at a temperature of 160° than at any other. Though they have nothing to do with each other, the high temperature which is necessary for pasteurization is desirable for separating, and two objects are thus attained by the one heating. After pasteurization and separation the milk is cooled down by being passed over a cooler of the Baudelot type-very similar to those used in breweries for cooling wort-through which well water is kept running, and is returned to the farmers for feeding calves, etc. The cream is cooled rapidly by being passed over a circular capillary cooler, through the corrugations of which well water is circulating. This reduces its temperature to about 70° F., which is about as low as it is possible to get it with ordinary well water, though in parts of Ireland, notably County Kerry, the temperature of the springs is much lower.

The more rapidly milk is cooled, the better for it and the longer it can be preserved. It is, therefore, desirable to still further reduce the temperature of the cream to about 50°. In view of the fact that the subsequent ripening again raises the temperature of the cream to 70°, this cooling might appear to be unnecessary, but it is not so, as any tendency to bacterial activity and the absorption of aerial ferments is counteracted by it. At this temperature, then, the cream is placed in vats, where it ripens. Practically it ferments, and, due to this lactic fermentation, the temperature, as stated above, rises. In from fifteen to twenty hours the cream is ready to be churned, but, in order that the fat globules may not be broken and the butter become oily, and in order also that the yield may be as large as

possible, the cream is again cooled by being run over a capillary cooler on its way from the ripening vat to the churn, which it reaches at a temperature of 48°. In some forty-five minutes churning is complete and the butter floats on the top of the whey in a fine firm condition.

This, then, is the process. The necessity for refrigeration will be seen in the low temperature which it is absolutely necessary to keep if it is wished to obtain the best results. It is desirable also to chill the butter and the milk before it is sent to market.

Fig. 1121 illustrates a small refrigerating machine and plant for cooling cream by means of a circular capillary cooler. The cream is run on to the distributing saucer from the ripening vats, and flows gently and evenly down over the wide flutings of the cooler into the collecting saucer at the bottom and away to the churn. Brine chilled in the evaporator of the refrigerating machine is pumped round through the flutings of the cooler and absorbs heat from the cream. The distribution of the cream over the cooler must be regulated so as to ensure its all being of an even temperature.

In some dairies the ripening vats are placed so as to command the churns, the cream being run from them over the cooler and into the churns by gravity. Where this is done, the regulation of the flow over the coolers is not difficult; but where for some reason or other the cream has to be pumped, care should be taken to regulate the suction of the pump to give an even flow.

The essence of a successful dairy is cleanliness, and great care should be taken to arrange that every vessel in

1 Messrs William Douglas & Sons, Ltd., Putney, London. A somewhat similar block has appeared in Ice and Cold Storage.

contact with the milk or cream can be thoroughly scalded down each time after it has been used.

Milk-cooling and Preserving.-Undoubtedly the surest precaution against disease in milk is pasteurization, but, though common in Denmark and in some of the Irish dairies where milk is heated up to from 200 to 212° F.,

this country has not yet advanced so far. The next best thing to pasteurizing the domestic milk supply is to cool it to a low temperature before it leaves the dairy. This is done by running it over a vertical milk-cooler constructed of fluted and tinned copper. The milk runs down the outside of the cooler in a thin stream and is cooled by refrig

CREAM

OUTLET

erated water or brine, which circulates inside the coils. The apparatus, in fact, is very much the same as that used in breweries for cooling wort.

Pasteurization, which only destroys full-grown bacteria, must not be confused with sterilization. The latter process consists of heating the milk up to some 200° F. to destroy the bacteria, cooling it down, and letting it stand until the bacteria spores which have not been destroyed have had time to develop. In order to destroy these spores, the process is then repeated. It is essential that during and after sterilization the milk should be protected from contact with the outside air. It is accordingly bottled in hermetically sealed bottles and offered for sale. After sterilization the milk will keep for any length of time, so long as it is not exposed to the atmosphere and the aerial ferments it contains.

THE CRYSTALLIZATION OF PARAFFIN.

During the process of distilling the natural oil shales, a number of oils of different specific gravities are obtained. With the more volatile kinds refrigeration is not concerned, but it is used extensively in assisting the crystallization of those which are solid at ordinary temperatures and which, when mixed with stearine, are extensively used for making candles. During the cold winter months no great difficulty is found in separating the heavy paraffin from the other oils, as it will crystallize out; but in the summer months the temperature is too high, and crystallization will not take place to its full extent. One of the first applications of refrigeration was to cooling paraffin in the summer, and a large saving was made by Kirk's machine, which was used for cooling oil in some works near Bathgate. Until comparatively recently the cooling of the oil and the

crystallization of the paraffin was brought about by revolving a drum filled with refrigerated brine in a tank containing the oil. The paraffin coming in contact with the cold metal congealed on its surface, and was scraped off the drum as it revolved. This process, though it ensured the rapid cooling of a large quantity of oil, was not satisfactory for the following reasons :—

The object of cooling paraffin-a process essentially of crystallization and filtration-is to separate efficiently the paraffin from the oil. This can only be done by allowing the paraffin crystals to grow to a considerable size, so that the oil will drain away from them. Owing, however, to the high average viscosity of the oil and the close interlacing of the crystals, about 75 per cent. of the oil cannot be separated by draining alone, and filtration has to be resorted to. For this purpose the solidified cakes of paraffin have to be broken up, and the oil contained between and round the crystals liberated. The paraffin, which still contains its crystalline formation, is then passed through a filter-press, which separates out the balance of the oil. The rapid cooling on a drum did not give the crystals time to develop, and consequently the paraffin was only very faintly crystalline, and, therefore, in the best possible position for holding a large quantity of oil in its bulk.

A number of experiments were made with the object of cooling the paraffin more slowly and by artificial means, but, owing to the very low conductivity of paraffin, the time and space required was found to be too great. About 1884 Mr Beilby started some experiments at Oakbank Oil Works, and economized space by having narrow deep coolers standing on their sides, instead, as had been previously done, of having shallow flat coolers resting on