Feb. 27, 1879] 



NATURE 



399 



concentration, vapours of methyl alcohol, methyl cyanide and 

 other nitriles, are given off, these are condensed and the 

 cyanide used for the preparation of ammonia and acetic acid by 

 decomposing it with an alkali, 



Trimethylamine itself is at present of no commercial value, 

 though we are not without hopes that a useful employment for 

 this substance may soon be found. The question arises as to 

 how this material can be made to yield substances capable of 

 ready application in the arts. This problem has been solved 

 by M. Vincent in a most ingenious way. He finds that the 

 hydrochlorate of trimethyla nine, when heated to a temperature 

 of 260°, decomposes into (i) ammonia, (2) free trimethylamine, 

 and (3) chloride of methyl : — 



aNMegHCl = 2NMe3 + NH3 + sMeCl. 



By bubbling the vapours through hydrochloric acid, the alka- 



C 



most valuable for preparing certain methylated dyes, which are 

 at present costly, inasmuch as they have hitherto been obtained 

 by the use of methyl iodide, an expensive substance. 



Methyl chloride was discovered in 1840 by MM. Dumas and 

 Peligot, who obtained it by heating a mixture of common salt, 

 methyl alcohol, and sulphu ic acid. It is a gas at the ordinary 

 temperature, possesses an ethereal smell and a sweet taste, and 

 its specific gravity is I "738. It is somewhat soluble in water 

 (about 3 volumes), but much more in acetic acid (40 volumes), 

 and in alcohol (35 volumes). It bums with a luminous flame 

 tinged at the edges with green, yielding carbonic and hydro- 

 chloric acids. Under pressure, methyl chloride can readily be 

 condensed to a colourless, very mobile liquid, boiling at - 23 C. 

 under a pressiu-e of 760 mm. As the tension of the vapour is 

 not high, and as it does not increase very rapidly with the tem- 

 j perature, the liquefaction can be readily effected, and the collec- 

 tion and transport of the liquefied chloride can be carried on 

 without danger. The following table shows the tension of 

 chloride of methyl at varying temperatures : — 



At 0° the tension of CH3CI is 2*48 atmospheres. 



Fig. I. 



line gases are retained, and the gaseous chloride of methyl passes 

 on to be purified by washing with dilute caustic soda and drying 

 with strong sulphuric acid. This is then collected in a gas- 

 holder, whence it is pumped into strong receivers and liquefied. 

 The construction of one of these is shown in Fig. i. They 

 consist of strong wrought-iron cyUnders, tested to resist a 

 pressure of 20 kilos per square centimeter, and containing 50, 

 no, or 220 kilos of chloride of methyl. The liquid is drawn 

 from these receivers by opening the screw tap (d), which is 

 covered by a cap (c) to prevent injury during transit. 



Both anmaionia and chloride of methyl are, however, sub- 

 stances possessing a considerable commercial value. The latter 

 compound has up to this time, indeed, not been obtained in 

 large quantities, but it can be employed for two distinct purposes 

 — I. It serves as a means of producing artificial cold. 2. It is 



Fig. 2. 



From these numbers we must of course subtract i to obtain 

 the pressure which the vapour exerts upon the containing vessel. 



As a means of producing low temperatures chloride of methyl 

 will prove of great sersdce both in the laboratory and on a larger 

 industrial scale. When the liquid is allowed to escape from the 

 receiver into an open vessel, it b^ns to boil, and in a few 

 moments the temperature of the liquid is lowered by the ebulli- 

 tion below — 23°, the boiling-point of the chloride. The liquid 

 then remains for a length of time in a quiescent state, and may 

 be used as a freezing agent. By increasing the rapidity of the 

 evaporation by means of a current of air blown through the 

 liquid, or better, by placing the hquid in connection with a good 

 air-pump, the temperature of the hquid can in a few minutes be 

 reduced to — 55°, and large masses of mercury easily sohdified. 



The construction of a small copper receiver and of the fireezing- 

 machine employed by M. Camille Vincent is shown in Fig. 2. It 

 consists of a double-cased copper vessel, between the two sides of 

 which the methyl chloride is introduced. The central space is filled 

 with some hquid such as alcohol, incapable of solidification. The 

 chloride of methyl is allowed to enter by the screw-tap (b), and 



