56 Professor Boscoe [Feb. 21, 



yielding carbonic and hydrochloric acids. Under pressure, methyl 

 chloride can be readily condensed to a colourless, very mobile liquid, 

 boiling at — 23° C. under a pressure of 760 mm. As the tension 

 of the vapour is not high, and as it does not increase very rapidly 

 with the temperature, the liquefaction can be readily ejffected, and the 

 collection 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° tlie tension of CH3CI is 2 -48 atmospherL^s. 

 „ 15° „ „ 4- 11 



„ 20° „ „ 4-81 



„ 25° „ „ 5 62 



„ 30° „ „ 6-50 



„ 35° „ „ 7-50 



From these numbers we must of course subtract 1 to obtain the 

 pressure which the vapour exerts on the containing vessel. 



As a means of producing low temperatures chloride of methyl will 

 prove of great service both in the laboratory and on a larger in- 

 dustrial scale. When the liquid is allowed to escape from the receiver 

 into an open vessel, it begins to boil, and in a few moments the tem- 

 perature of the liquid is lowered by the ebullition below —23°, the 

 boiling point of tbe 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 liquid in 

 connection with a good air-pump, the temperature of the liquid can in 

 a few moments be reduced to —55°, and large masses of mercury 

 easily solidified. The construction of a small freezing machine em- 

 ployed by M. Camille Vincent is shown in Fig. 2. It consists of a 

 double-cased copper vessel, between the two casings of which the 

 methyl chloride (A) is introduced. The central space (M) is filled 

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

 chloride of methyl is allowed to enter from the cylindrical reservoir 

 by the screw tap (B) and the screw (S) left open to permit of the 

 escape of the gas. As soon as the whole mass of liquid has been 

 reduced to a temperature of — 23°, ebullition ceases, the screw (S) 

 may be replaced, and if a temperature lower than — 23° be required, 

 the tube (B) placed in connection with a good aiv-pump. By this 

 simple means a litre of alcohol can be kept for several hours at tem- 

 peratures either of — 23° or — 55°, and thus a large number of ex- 

 periments can be performed for which hitherto the expensive liquid 

 nitrous oxide or solid carbonic acid was required. 



M. Vincent has recently constructed a much larger and more 

 perfect and continuous form of freezing machine, in which by means 

 of an air-pump and a forcing pump the chloride of methyl is evaporated 

 in the freezing machine and again condensed in the cylinders. This 

 enlarged form of apparatus will probably compete favourably with the 



