CORRESPONDENTS who expect to receive answers to their letters must, in all cases, sign their names. We have a right to know those who seeJcin-formation from us; beside, as sometimes happens, we may prefer to address correspondents by mail. SPECIAL NOTE.—This column is designed for the general interest and instruction of our readers,not for gratuitous replies to questions of a purely business or personal nature. We will publish such inquiries, however -when paid for as advertisemets at $1*00 a line, under the head of "Business and Personal." $WAH reference to bach numbers should be by volume and page. J. M., of N". Y.—To ascertain the amount of horse power which is the equivalent of the steam delivered through a pipe into a tank containing water, the best way for you will be first to ascertain the evaporative power of your boiler in relation to the amount of fuel consumed. From this you can ascertain the horsepower of your boiler and the amount of fuel it takes per horse power. Then ascertaining the amount of fuel saved by cutting off the tank during a given time, under average circumstances you can compute from that the horse power delivered. P. D., f Va.—Straw is bleached by simply exposing it in a closed chamber to the fames of burning sulphur. An old flour barrel is the apparatus most used for the purpose by milliners ; a flat stone being laid on the ground, the sulphur ignited thereon, and the barrel containing the articles to be bleached turned over it. There is no English work on chemistry applied to the arts fully up to the times. Muspratt's chemistry is perhaps as good as any. H. R., of 111.—The diagram you send us and the explanation accompanying it lead us to suppose that in the construction of your trunk a too common error has been committed. Both the ipes and the wooden trunk are too small, to give you water enough when the level in the dam is low ; you shouldincrease their capacity to 400inches and put a stand pipe in your bulk head as high as the level in your dam when it is fall. This will remove the difficulty. C. E. R., of 111.—The exact hight of a column of mercury that will be sustained by a pound of pressure per square inch anywhere, is a column that contains one pound of mercury for every square inch of its base, provided the column be of equal size throughout. This hight will vary for all different temperatures, the question you ask us cannot therefore be more definitely answered. B. J. H., of Mo.—The traveling glass blowers use gas sometimes, but more commonly s;ood sperm or lard oil burned in a lamp with a large wick, perfect combustion being secured by means of a foot blowpipe. The glass used is a peculiar kind of soft glass made specially for that and other purposes. It can lee purchased of dealers in chemical apparatus. E. E. W., of N. B.—We find upon inquiry of practical rubber men that the difficulty you experience in getting your cement, made by dissolving rubber in naphtha, to\harden readily, is not met with by them, and they do not use any other substance to accelerate the hardening. The benzine in evaporating leaves pure rubber and of course it possesses the usual elasticity of that material. W. H. S., of Pa., asks if we can inform him of any substance that will keep insects from destroying an entomologist's collection. According to the Entomologist, the insects which do the principal part of destruction in cabinet specimens are small beetles, difficult of extermination. As a preventive none but very tight boxes should be used for the cabinet. Camphor should be always kept in the boxes and the specimens frequently examined. When a collection has been attacked pour a solution of corrosive sublimate on the cottom of the boxes. It will kill all the bugs that touch it. L. H. H., of Vt.—We see no reason why you should not be able to remove borax, after brazing, Vith simple hot water. There occasionforusingnitricacid. Are you not Mistaking the film of solder for borax ? J. K., of N. Y.—You must use more tin in your solder to get the required brilliancy, from \% to 2 parts tin to 1 of lead, instead of .equal parts each. S. W. R., of Mass.—We understand that the term " monkey " as applied to a hand wrench is merely a nick-name. Its use is entirely meaningless so far as we know. C. C. H. of Kansas.—Your suggestion to support foot bridges across rivers by means of balloons is not new. It is impracticable. J. B., of N. J.—Permanent agencies for the general sale of patents have not been very successful. One good invention will usually occupy the undivided attention of the agent until it is sold. Hence the difficulty of keeping a shop full of models.