ON ARTIFICIAL REFRIGERATION. 017 



32° Fahr., and to bo. a^ain dissolved" in the central chamber. To pro- 

 duce "intense degrees of cold in the apparatus," a small quantity of ice 

 or snow is put into the central chamber. 



In 1858, Mr. Siemens improved the construction of the refrigerator 

 in this machine, and in the system of evaporating the spent solution for 

 the purpose of recrystallization or reproduction of the salt or compound 

 which has been dissolved. He used evaporating-pans over a furnace, 

 or the flues thereof, in such a manner as to afford the means of drawing 

 off the contents of one or more pans into one or more other pans. 



Another device for revolving ice-moulds with a freezing-mixture around 

 them was patented in England, in 18G2, by Giovanni Battista Toselli, 

 and this form of apparatus is being sold in Paris. The invention consists, 

 first, in the vertical rotation of the liquids to be congealed ; secondly, 

 in the very simple shape of the machine with concentric sides and oi)po- 

 site openings, whether such machine be made in whole or in x>art of 

 metal ; thirdly, in the said machines being suitable for the production 

 of ice by chemical means. 



M.— GASES AND THEIR LIQUEFACTION. 



Van Helmont introduced the word " gas," and in 1752 he established the 

 existence of gas sylvestre (carbonic acid), which Black, three years later, 

 termed fixed air. To Van Helmont is due the distinction between a gas 

 and a vapor. Aeriform fluids would not liquefy in cooling, whereas, 

 vapors, he said, required heat to maintain them in the free molecular or 

 gaseous state. 



Daniel Bernouilli first stated that gases are formed of material parti- 

 cles, free in space, and animated by very rapid rectilinear movements. 

 The tension of elastic fluids results from the shock of these particles 

 against the sides of the containing vessels. The gaseous molecules 

 manifest the energy of motion termed kinetic (from z?v^w, I move). 

 Lucretius held that the different proi^erties of matter depended on such 

 a motion. The law of Boyle or of Mariotte follows as a natural conse- 

 quence of this idea, and it is this law which interests specially all those 

 w^ho are engaged in the liquefaction of gases and the abstraction of heat 

 by these from surrounding objects, as they return to the gaseous state. 



As Professor Wurtz puts it in a recent lectiu-e : * " Suppose a gas occu- 

 pying a certain volume, and composed of a definite number of material 

 particles, or molecules, so called, to be contained in a closed vessel, such 

 as the cylinder of an air-j)ump, the xJressure on the piston will be deter- 

 mined by the number of shocks of the molecules diffused through the 

 neighboring stratum of gas. If, then, the volume of gas be reduced, the 

 number of particles in this layer will be increased as well as the sum of 

 the shocks, and the pressure will be increased in proportion thereto. 

 Temperature is determined by these movements of gaseous molecules. 



* On tlie constitution of matter in the gaseous state, being tlie Faraday lecture deliv- 

 ered November 12, 1878, at tlie Royal Institution, London. 



