layer of sheathing-paper. One side of the hollow cylinder is cut lengthwise, and to apply it to the pipe, the meeting edges are drawn apart, the cylinder sprung upon the pipe, and fastened with double-pointed tacks. The joints are covered by bands of sheathing-paper. Weight, with 6 double-pointed tacks, 284 ounces per linear foot. Diameter 41⁄2 inches.

6. Bradley's Insulated Air Covering, made by Shields & Brown, New York.-Hollow cylinders 3 feet long, consisting of nineteen layers of stout paper. Nearest the pipe is a sheet of asbestos paper, next two sheets of sheathing-paper, one sheet of asbestos paper, two of sheathing paper, another of asbestos paper, and twelve more of sheathing-paper. The sheathing-paper is alternately smooth and pressed or embossed. The cylinders are placed upon the pipe, the edges drawn together and secured by double-pointed tacks, and the joints sealed with strips of paper. Diameter 41⁄2 inches. Weight, with tacks, 274 ounces per linear foot.

7. Reed's Pipe Covering.-Paper cylinders composed of about twelve sheets of paper, the inner one of which is asbestos paper. The covering is applied in the same manner as No. 5, by forcing open the edges and springing upon the pipe. Diameter 44 inches. Weight, with tacks, 2634 ounces per linear foot.

8. Fossil Meal Pipe Covering, from the Fossil

Meal Company, New York.-A dry mixture of diatomaceous earth with organic fiber (hair, manilla, etc.). Contains probably also some starchy material like flour. It is mixed with water and applied to the pipe with a trowel. Diameter of covering 334 inches. Weight 24

ounces per linear foot.

Six feet of each of these coverings was applied in the proper manner to the inclined pipes. The pipes were parallel and placed at such intervals that about three inches space intervened between the coverings. They all received their steam from the main steam pipe, of which they were branches. At each end of the series was an extra pipe, also covered, which served to place the first and last of the coverings under trial in as nearly as possible the same circumstances as the others. The pipes were located in a small engine-room adjacent to the boilerroom; the doors and windows were kept closed, so that there should be no drafts of air during the trials. On the mornings of the days of the trials, the steam was admitted into the apparatus, the stopcocks being closed. At the end of each hour, the water condensed in the pipes was drawn off into graduated cylinders and measured. It was found that during the forenoon the condensations became less each hour, and it was not until 2 or 3 o'clock in the afternoon, when everything was heated to the maximum, that the

condensations became uniform. At this point the conditions of actual practice were established, and the rate of condensation then existing is that by which we have to judge the efficiency of the different covering materials. The trials were continued several days, and there was no material difference between the results obtained during the different days. The pressure of steam ranged between 65 and 75 pounds to the square inch during the trials, and the temperature of the room was about 70°F. The condensation within the caps, which were well wrapped with cotton-wool, was unimportant with respect to that of the 6 feet of pipe, and was disregarded in calculating the results. The condensation in the differently covered pipes was as follows:

The average temperature of the steam being 150.5° C. (302.9° F.), its latent heat was 501.9° C. (935.4° F.). The condensation in No I was 34 grammes per foot per hour. We have, then, as the loss by condensation, 343 X 501.9 X 1000

18.39 kilogram-Centigrade heat-units per foot hour. In the same way we may deduce for the other materials:

per

18.97 kilogram-centigrade heat-units per ft. per hr.

66

These results may be reduced to pound-Fahrenheit heat-units by multiplying by g × 2.205. This gives for:

No. I.

. 69.02 pound-Fahrenheit heat-units per ft. per hour.

From these experiments it appears that, of the materials tried, the hair-felt covering was the most non-conducting. The magnesia covering ranked next, and close upon it came the mineral wool. Following this came the paper coverings, and finally the fossil meal.

All non-conducting materials may be divided, with respect to their composition, into two classes: 1st, Those composed essentially of or

ganic substances, as hair, paper, straw, etc.; and 2d, Those consisting of natural or artificial mineral substances, as asbestos, magnesia, slag-wool,

etc.

Of all the organic substances that have been employed as non-conductors, there is probably none that merits recognition as a covering material for hot steam-pipes. This fact has been more saliently thrust upon the attention of steam-users from year to year, by the fires the origin of which is ascribed to the combustibility of this class of pipe-covering materials. The solicitude of the insurance companies has been enlisted in the subject, and they have repeatedly instituted very exhaustive investigations by scientific men, whose reports on these experiments form the major part of the literature of non-conducting materials. Several of these materials, the paper coverings especially, are known to have taken fire spontaneously after being exposed for a long time to the heat of pipes carrying steam under ordinary pressures. And those of the organic materials that do not burst into flame under the conditions prevailing, are, with few exceptions, subject to deterioration by charing, which proceeds with a rapidity and to an extent that depends upon the temperature of the steam used. Aside from the possible danger of conflagrations from these charring and tinderlike substances, the changes which they undergo