hardened. For valve parts, three per cent. nickel-steel, because of its resistance to corrosion, low coefficient of expansion, and other physical properties, is recommended. Cams and tappets have been made of special alloys, but carbon steel also gives good results. Unquestionably there are important advantages to be gained by the use of metal propellers, and, as a solid section seems desirable, it seems quite certain that some light-weight alloy will prove superior to steel. The design in the power and transmission plants should be made first, and then, if necessary, the elastic limit increased by the use of chrome-nickel-steel. On short flights the engine and transmission parts weights are of more importance than the amount of lubricating oil, while on long flights the increase in weight by the use of cast-iron cylinders and pistons will very likely be more than offset by the saving in weight of lubricating oil. When it comes to the question of aeroplanes for military use it is of the greatest importance that the passengers and vital parts of the machine be protected as far as possible by armor plate. It is impracticable to use armor plate of sufficient thickness to withstand all kinds of shell fire on account of the weight. On the other hand, however, it is possible to secure some remarkably satisfactory results with very thin plate. Nitro-starch a s a n Explosive. S. S. SADTLER. (Metallurgical and Chemical Engineering, vol. xvi, No. 7, P. 36r, April I, I917.)-The application of high explosives to mining and general commercial purposes may be said to date from the discovery of Nobel that nitroglycerin could be absorbed in kieselguhr and then handled with a sufficient degree of safety to warrant its use. The product was called dynamite, but this name now applies broadly not only to nitroglycerin absorbed by other inert materials, like sawdust, mica-powder, etc., and other mixtures as well, but also it applies to various high explosives containing no nitroglycerin. At present there are an indefinite number of chemical mixtures aiming to meet the different working conditions. By the solution of gun-cotton or nitrocellulose in nitroglycerin (in which it readily dissolves, forming a jelly-like mass) we obtain blasting gelatine and gelatine dynamites and mixtures of these with other ingredients. Gun-cotton (or the higher cellulose nitrate) has not been found applicable by itself for the field of commercial blasting and mining explosives, except for submarine blasting, where the compressed gun-cotton finds a use, as it is too bulky in comparison to its weight for other work. An earnest effort had been made for some time to find a satisfactory substitute for nitroglycerin dynamite, but without success until recently, when great improvements were made in the manufacture of nitro-starch and a suitable container found for its use. Starch, which has an analogous chemical composition
[J. F. I.
to cellulose and forms corresponding nitrate esters, was early suggested as the basis of a high explosive, having all the advantages of cotton w i t h o u t its bulk or higher cost. F o r blasting, this material has great m a n y advantages. It cannot be exploded except by exploding a cap in contact with it, it gives off no bad fumes, is non-freezing, and appears to have good stability, a q u a n t i t y stored for ten m o n t h s shouting no deterioration. One of the chief points of merit in the use of nitro-starch is its cost. As there is no special difficulty in its manufacture, it can readily be seen that, being made from a base costing 2I~ to 2 ~ cents a pound, as compared with glycerine at 3 ° to 6o cents a pound, or cellulose rising to Io cents, there is great e c o n o m y in its use. Quite apart from the cost of bases, but for reasons of simplicity of handling and time of nitration, it promises to be more easily and economically m a n u f a c t u r e d than nitrocellulose.
Explosions in Oxygen Tanks. ANON. (Metallurgiccd and Chemical Engineering, vol. xvi, No. 7, P. 402, April I, x9r7. ) T h e attention of the Bureau of Mines has recently been directed to a series of explosions of o x y g e n made by the electrolytic process in which life has been lost as a result of h y d r o g e n being mixed with the oxygen. It has been found that this is due to improper design in the m a n u f a c t u r i n g apparatus (i.e., to the cells and electrical c o n n e c t i o n s ) ; to insufficient safeguards connected with the electric apparatus, the polarity suddenly and unexpectedly shifting; to the m a n u f a c t u r e of o x y g e n w i t h o u t f r e q u e n t analyses, and to incompetent and ignorant attendants. Unfort u n a t e l y certain makers of oxygen-building apparatus have advertised that any- laborer can take care of their apparatus. It is believed that the m a n u f a c t u r e of electrolytic o x y g e n can be carried on in a m a n n e r to make it perfectly safe. In fact, there must be over nine per cent. of hydrogen with the oxygen to make an explosive mixture. Nevertheless, certain tanks from one batch caused three widely-separated explosions in California, killing seven men in all, and an analysis of gas from a tank filled at the same time showed that it contained over 50 per cent. of hydrogen.
Census of Mining Engineers and Metallurgists in the United States. V a ~ H. MaZ~'NING. (Circulc~r letter, U. S. Burea:u of Mines, April 5, I 9 1 7 . ) - - T h e Bureau of Mines, in co6peration with the American Institute of Mining E n g i n e e r s and the A m e r i c a n Chemical Society, has u n d e r t a k e n a census of mining engineers, metallurgists, and chemists with a view of ascertaining the qualifications of each and the line of work in which each can be of the most service to the c o u n t r y in time of emergency. T h e classification will embrace 27 specific groups of industrial chemists, 16 groups of engineering specialists, and 15 groups in the metal-