refractive power; and of cerium alloyed with iron in substitution for the old flint and steel in kindling fire.
Marked progress has been made in devising synthetic methods of manufacturing some of the simpler carbon compounds hereto- fore obtained only from natural products. Thus formic acid has been prepared, on a considerable scale, by combining car- bonic oxide with caustic soda, under pressure one of the earliest syntheses effected by the French chemist Berthelot.
Acetylene, another discovery of this chemist, has been con- verted into alcohol, on the large scale, by processes also due to his acumen, by passing acetylene, prepared from calcium carbide together with hydrogen over a suitable catalyst thus producing ethylene, C2H 4 = C 2 H 2 -|-H 2 ; then absorbing the ethylene in sulphuric acid of suitable strength and distilling with water, to hydrolize the sulphate that is formed C 2 H4+H 2 S04 = C 2 H 5 . HSO 4 !|C 2 H 5 . HSO 4 +H 2 O=C 2 H 5 O+H 2 SO 4 . The process is said to have been an economic success, in Italy, where water-power is available. The process has also been carried out experimentally with coke-oven gases as a source of ethylene.
During the war, much acetic acid was made from alcohol by first converting this into aldehyde and hydrogen, by passing the vapour over heated copper; then oxidizing the aldehyde by means of air, in presence of a manganese salt. Acid so made is of better quality than that from crude calcium acetate. Acetic acid has also been produced by oxidizing aldehyde prepared directly from acetylene, through the agency of sulphuric acid acting in conjunction with mercuric and ferric sulphates; oxygen distilled out from liquefied air has been used in the process. The cost of acid prepared in this way, in one of the chief German works, in 1919, is stated to have been 50 per ton. The impor- tance of acetic acid is now far greater than it was, owing to the use that has been made of it in preparing varnishes or dopes for airplane cloth. The attempt is also being made to develop the manufacture of artificial silk from acetylcellulose.
The manufacture of explosives has involved various other developments. Prior to the war, the acetone used as a solvent, in making the propulsive cordite a mixture of the trinitrates produced on supernitrifying glycerol and cellulose was obtained by the dry distillation of calcium acetate, this being made from the crude acid which is obtained, in carbonizing wood, together with wood spirit or methylic alcohol. When a shortage of the supply of acetate was imminent, two new methods of making acetone were developed one involving the passage of acetic acid vapours over heated alumina (2CH 3 . COOH = CH 3 . CO. CH 3 +CO 2 +OH 2 ); the other the fermentation of glucose by a special organism giving rise to a mixture of acetone and normal butylic alcohol. Success was found to depend on the use of a pure organism and at first much difficulty was experienced in steriliz- ing the large bulks of liquid used: two of the organisms were not killed until the temperature was raised to 130.
Acetone was originally used in making cordite, because it is a solvent of cellulose trinitrate. Another way of overcoming the difficulty, created by the shortage of the solvent, was found in the use of a less nitrated cellulose, soluble in a mixture of ether and alcohol. This departure involved the manufacture of ether not by a new method but on an unprecedented scale, without any difficulty. Another substance made on a scale which might previously have seemed inconceivable was hydrogen cyanide or prussic acid. Experience showed that any desired substance may be made on any desired scale, putting economic cost aside.
Hitherto, glycerol has always been obtained from natural fats, usually as a by-product of the manufacture of soap. It is a constant product of the fermentation of glucose by yeast in the brewing process, although only about 3% of the sugar used takes this form. Experiments carried out in America and Ger- many, during the war, showed that the proportion might be raised even to 20% by carrying on the fermentation in presence of an alkaline sulphite or carbonate. If needs were, therefore, glycerol might be manufactured from starchy materials.
A point of interest in connexion with explosives was the use during the war, for the first time, of Borneo petroleum as a source of much of the toluene required for the manufacture of trini-
trotoluene (TNT). Previously, toluene had been obtained only from coal tar. The presence of this and similar hydrocarbons in petroleum was first noticed by Hugo Muller and Warren De la Rue. The complete nitration of toluene to TNT is a matter of some difficulty. As proof of the value of scientific insight and the practice of a rigid scientific method in manufacturing indus- try, the fact may well be mentioned here that the most efficient British works for the production of this explosive, although only a small one, in point of quality of product and cost of production, was one established, at a very early date, by a Scotch professor and a young colleague versed in physical chemistry.
The explosive picric acid or trinitrophenol was also made on a large scale, not only from phenol extracted from coal tar but also from synthetic phenol, prepared by sulphonating benzene and fusing the sulphonate with caustic soda (C6H 6 +H 2 SO4 = C 6 H S . SO 3 H+OH 2 ; Ph. SO 3 Na+Na OH = Ph. OH+SO 3 Na 2 ). In England and France the old, barbaric, wasteful process of nitrating the phenol was unfortunately followed and the manu- facture was never put on a scientific footing. A substantial amount was made, however, by a very superior process, involving the conversion of benzene, C 6 H 6 , first into chlorobenzene, C 6 H 5 C1, then into dinitrochlorobenzene, C 6 H 3 (NO 2 ) 2 C1, next into dinitrophenol, C6H 3 (NO 2 ) 2 -OH, finally into trinitrophenol, C6H 2 (NO 2 ) 3 -OH. The operations are all carried out with ex- treme ease and except the first afford all but quantitative yields.
Many substances were made for the first time on a large scale during the war, and used as " poison gases " and to excite weep- ing; among the latter was chloropicrin, produced by " chlorinat- ing " picric acid, in presence of soda. The one which became of most consequence, the so-called mustard gas, really a by-no- means easily volatilized liquid, was always manufactured by the Germans by a rather involved process devised by Victor Meyer, which was never brought into operation, in an effective manner, elsewhere than in Germany. Shortly before the Armistice was declared, however, a far simpler method was developed, in England, which involved merely chlorinating sulphur and then passing ethylene into the chloride:
S 2 C1 2 +2C 2 H 4
C 2 H 4 C1 = C 2 H 4 C1
[s+s
Very large quantities had been prepared for use in the field, just before the war came to an end. No difficulty was experienced in preparing any desired quantity of ethylene, by heating alcohol with phosphoric acid.
Two substances have acquired importance, the one as a detonator, the other as a primer in starting the ignition of the less sensitive TNT, lead azide, Pb(N 3 ) 2 , and trinitrophenyl- methylnitramine, C 6 H 2 (NO 2 ) 3 .N.(CH 3 ).N0 2 . The former has the advantage that it is stable under the high temperature con- ditions of the East, where mercuric fulminate, the detonator commonly used, cannot be kept long. Prior to the war, the acid HN 3 , from which the azide is made, was little more than a chemical curiosity and almost feared on account of its instability. The nitramine referred to was made preferably from methylani- line but chiefly from dimethylaniline, two substances much used in the dyestuff industry.
Attention has been directed very frequently, of late years, to the production of a substitute for indiarubber. Thus far the German manufacturers have not been able to control the final stage of the process, that by which the simple hydrocarbon used initially is converted into the rubber complex. The " poly- merization " is effected only gradually and at a slow rate; in fact, the material is merely placed in hermetically sealed barrels and allowed to remain undisturbed, during six months, at about 32C., the rubber being finally obtained as a white spongy mass which has to be bored out of the barrels. The minimum cost of production appears to have been about i8s. per pound. The Germans went so far, however, that they organized the manu- facture on the scale of a possible output of i ,000 tons per month. The opinion that prevails is that the process cannot under any conditions be an economic success, until it can be controlled and much accelerated; it is dangerous to assume that this will
