DU MOTAY'S PROCESS OF ICE-MAKING. 797 



ploying those substances that are capable of producing the greatest 

 degree of cold. But a difficulty is encountered in the high pressures 

 of the gases produced in the pump, as there is no evading the physical 

 fact that the cold-producing power of a gas is a concomitant of its 

 tension, or pressure varying directly therewith. Thus, ammonia, with 

 a pressure at rest of eight atmospheres, and at work of twelve to 

 twenty atmosjAeres according to the temperature, is an excellent 

 refrigerant, but the use of a gas with such a high pressure is attended 

 with obvious drawbacks. At the other end of the scale is ether, 

 which is manageable at a low pressure, viz., zero at rest, and ten to 

 fifteen pounds per square inch at work ; but this advantage has its cor- 

 responding drawback, in accordance with the law above mentioned, 

 i. e., a comparatively low refrigerating power. It is, moreover, inflam- 

 mable, and, in contact with any of the lubricants used on the pump- 

 piston, there results an unintended product of soap, which, coating 

 the parts of the mechanism, obstructs the passage of the latent heat 

 from the circulating medium employed for freezing. Midway be- 

 tween these two agents, as regards its pressure, is sulphurous acid. 

 This gives a high degree of cold, its pressure at work being three and 

 one half to six atmospheres, and a little over two and one half atmos- 

 pheres at rest. Aside from its rather high pressure, a serious objec- 

 tion to its use is the liability to corrosion of the parts on contact of 

 the liquid with moisture, sulphuric acid being thereby produced, 

 which rapidly wears away the more important parts of the mechanism 

 employed. 



The various defects enumerated, and others incident to the use of 

 other agents not here particularized, viz., liability to explosion, inflam- 

 mability, indifferent refrigerating capacity, high vacuum, high press- 

 ure involving rapid wear and tear and danger in use, and other more 

 or less serious drawbacks, have made the attainment of a still better 

 system than the best of those referred to imperative. The great 

 desideratum, it will be seen, has been a process admitting of using 

 some of the better cold-producing agents without the dangers or an- 

 noyances due to the high tensions of their gases, or to other peculiari- 

 ties of their composition. The discovery of a method by which this 

 object could be attained is due to the genius of the late C. M. Tessie 

 du Motay. 



This eminent French chemist, acting on the suggestion of one of 

 his associates, M. Etienne Gillet, a gentleman who had made a close 

 study of artificial ice-making, sought to combine two or more liquids 

 which should have the property, in combination, of mutually neutral- 

 izing the defective features they exhibited when used separately, and 

 which should at the same time retain their desirable qualities. He 

 instituted experiments, in conjunction with M. Auguste Rossi, which 

 resulted in the discovery that ether, Avhen combined with sulphurous 

 acid, furnished a compound absolutely free from any of the defects 



