(8) J. H. S. wants a good receipt to prevent hair coming out. A. Scald black tea, 2 ounces, with 1 gallon of boiling water, strain, and add 3 ounces glycerine, tincture cantharides ½ ounce, bay rum 1 quart. Mix well and perfume. This is a good preparation for frequent use in its effect both on the scalp and hair, but neither will be kept in good condition without care and attention to general health. See articles in SUPPLEMENTS, 102, 388, 396. (9) A. H. asks the size of steel wire rope necessary to suspend a weight of 16,000 pounds, each end of the rope being fastened 1,600 yards apart, the weight to travel from one end to the other on the rope. A. The scheme of so long a span carrying a load is impracticable. A span of 4,800 feet will nearly absorb the margin of safety by its own weight, depending upon the amount of deflection that could be allowed in the catenary curve. The largest steel cables that are made, 2⅝ inches, weigh 13 pounds per foot, or over 31 net tons for your span; with a deflection of one twenty-fifth, or nearly 200 feet, the tension would be 3¼ times the weight, or 254,800 pounds, while the ultimate strength is but 400,000 pounds. (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.