(10) G. A. L. asks: Why will a brake on the hind end of a train of cars hold more than a brake set ahead of it on train? A. We do not know that it is so. It is possibly a fancy.
(11) A. K. H. asks: Will hot air cool off by sending it rapidly through a wooden tube 300 or 400 feet long? If so, how much? A. Yes, slightly. An iron pipe is better if you wish to cool the air. How much the air will be cooled will depend on initial temperature and the temperature of the conductor and surrounding air.
(12) H. H. writes: I have large quantities of iron and steel to pickle, or, in other words, to clean. I use oil of vitriol, which is expensive and dangerous. Is there an acid that would be cheaper and at the same time as effective? A. We know of nothing cheaper or better than sulphuric acid for pickling castings. The most economical method, as practiced here, is found in the hot bath, a tub lined with lead, or if of small requirement a stone pot. Water 5 to 8 parts, acid 1 part. Boil the work in the acid bath for a few minutes, then rinse in hot water. There is no danger if properly managed. For wrought iron and steel, use hydrochloric acid and water.
(13) W. F. E. asks: 1. How are bath bricks made? A. Bath bricks are found native as minerals, and are imported from England. 2. How are papier mache ornaments moulded, and where can I procure a work on the subject? A. We can send you Spons' "Workshop Receipts" for $2.00, first series, which contains full information on papier mache. See also various articles in SCIENTIFIC AMERICAN SUPPLEMENT on the technology of the paper trade.
(14) W. M. S. asks how to make liquid glue. A. Take a wide mouthed bottle, and dissolve in it 8 ounces best glue in ½ pint water, by setting it in a vessel of water, and heating until dissolved. Then add slowly 2½ ounces strong nitric acid 36° Baume, stirring all the while. Effervescence takes place, with generation of fumes. When all the acid has been added, the liquid is allowed to cool. Keep it well corked, and it will be ready for use at any time.
(15) E. H. F. asks what preparation steam laundries use to make their goods so stiff and have such a fine gloss, and how is it used, and, if used with starch, is hot or cold starch used? A. Melt 2½ pounds of the very best A 1 paraffine wax over a slow fire. When liquefied, remove from the fire and stir in 100 drops oil of citronella. Have a lot of round new pie tins, clean and nice; place them on a level table, coat them slightly with sweet oil, and pour about six tablespoonfuls of the enamel into each tin. The pan may be floated in water to cool the contents sufficiently to permit the mixture to be cut or stamped out with a tin cutter into small cakes about the size of a peppermint lozenge. Two of these cakes added to each pint of starch will cause the smoothing iron to impart the finest possible finish to muslin or linen, besides perfuming the clothes.