All reference to back numbers should be by volume andpage. D. G. 0., of Mass.—Deby, in his “ Steam Vade Mecum,” gives the following rule for calculating the temperatures of steam at different pressures: “ Substract the Cen. units of latent heat from 606*5 and divide the remainder by 0*695. Thisgives the temperature in Cen. degrees of the thermometer. This rule is based upon a law which that author claims to have discovered, namely, that the pressure ot steam in atmospheres in a close vessel increases in a geometrical progression, the ratio of which is two, while the latent heat (so called) decreases (is in reality converted into other modes of motion) in a compound arithmetical progression, the constant ofwhich is 17 Cen. units or 30'6 Fah. units, and the multipliers, respectively, as the numbers 1, 2,3, 4,5, etc. We do not regard this law as fully established. Since Its publication, on page 246, Vol. XX., of the SCIENTIFIC AMERICAN, it has, however, met with neither denial nor confirmation. It is certain, however, that the rule above given, secures results which coincide with the results of previous experiments to within a very close approximation. You will find these results in tabulated form, in the work above mentioned, published by Willis, McDonald&Co., 141 Fulton street, New York, and nearly the same in other works on heat and steam. Loose sawdust would, we think, be more likely to take fire from proximityto hot steam pipes than solid wood. J. T. K., of Wis.—The horse power of a boiler is computed from the extent of its heating surface. In good boilers, with furnaces so arranged, that good combustion and utilization of the heat is secured, it is common to allow for marine flue boilers, 8 square feet of heating surface per horse power; for marine tabular boilers, 9 to 10 square feet; and for locomotive boilers 6 square feet. Stationary boilers vary greatly in this respect. They oftener, we judge, require twelve feet of heating surface than less,and it is evident that the results attained with any boiler must depend in great measure upon collateral circumstances. The best constructed boiler might give poor results under unfavorable circumstances of setting, etc. You will noiv see that you have not given us the data for computing the heating surface of your boiler, and that we can not therefore give you the horse power. The amount of water which can be raised from 50 deg. Fah. to 212 deg. Fah. perhorse-power of a boiler, by the use or' a pipe and steam jet, is approximately six cubic feet per hour, M. S., of 1ll.—The horse-power of an engine is equal to the ,mean effective pressure per square inch of piston area inpounds multiplied by the number of square inches in that area, multiplied by the length ofstroke in feet, multiplied by the number of strokes per minute, and divided by 33,000. It is rare.that in engines worked non-expansively, the mean effective pressure in the cylinder can be considered as equal to the boiler pressure ; but assuming it to be nearly so in your case, where the cylinder is 14 inches internal diameter and stroke 20 inches, boiler pressure 80 pounds, and numbtV of strokes per minute 101*25, the horsepower would be 80 X (143 X 0'7854) X 1'666 X 101'25 + 33,000, which you can work out for yourself. S. R., of N. J.—You can bleach your ivory veneers by exposing them to the action of chlorine. To make this gas, put into a glass retort or flask, a mixture of 18 parts common salt and 15 parts finely pulverized binoxide of manganese, and pour upon the mixture a cold mixture of45 parts strong sulphuric acid and 21 parts of water. The gas will immediately come over, and you may conduct it into a close cask, set out of doors and away from your shop, as this gas is injurious to inhale. When the evolution of gas slackens, a gentle heat applied to the retort will immediately increase it. The veneers should be laid on racks, or otherwise kept apart, so that they may be uniformly acted upon. G. T., of Tenn.—Ink cannot be considered as a solution. It is a fluid containing coloring matter in 8u8pension; Usually this coloring matter is gallate of iron, or a compound of gallic acid, extracted from the nutgalls employed inits manufacture, and the oxide of iron. T. D. G., of Ohio.—The black color of caoutchouc (gum-elastic india-rubber) is acquired from the smoke of fires used in its desiccation after the juice is extracted from the trees. It is not a natural property of this substance, which, in a pure state, is ofa white color. J. K. A., of Mich.—The tenus “ nucleus” and “nebulosity,” are used in astronomy to denote entirely distinct parts of a comet. The nucleus is what is commonly known as the head, and the nebulosity is the attenuated matter whichsurrounds the true nucleus. o R. M. Van N., of_Neb.—A patent was taken out in 1823, for the use of cork tree bark, for dyeing cotton, wool, and other tissues, nankeen. We do not think the process was ever extensively used, and we see nothing new.ln the method you employ. H;"C. P., of Texas.—Your application of horn platesto a “ coat of mail,” a term which is hardly applicable, is very ancient. Such plates may be made quite effective as a protection from sword thrusts or bullets, but there is nothing mew in the idea you have conceived. D. B. L., of Ala.—Your toy gun is, we think, a decided novelty, and of cowse, as such, patentable. Large sums have been realized by patentees of toys. A unique and taking affair like yours would be sure to have a run. R. T. M., of Mo.—The fact that sour apples attack the teeth more than vinegar, is owing to the presence of malic acid in such apples, which acts upon the enamel of the teeth much more than dilute acetic acid—vinegar. A. B. F., of Mass.—As “ working engineer,” you should be able to obtain the different brands, trade marks, etc., of boiler iron without expecting us to do a liberal amount of gratuitous advertising for your especiai benefit. A. C. B., of Mass.—We can recommend nothing as being better than plumbago, for coating insects, and other small and delicate objects, in the process of electroplating • J. R., of —., “ Pallett's, Millers, Millwrights, and Engineers' Guide"#is the book you need. Published by Henry Carey Baird, Philadelphia. R. B., of Ala.—One part of Portland cement and eight of sand would make a good lining for an artificial duck pond.