March 30, 1876] 



NATURE 



43; 



The high price at which it is sold prevents many people 

 from buying it. It is for the purpose of rendering the 

 supply of this useful and healthful article abundant and 

 cheap that ice-making machines have been devised. These 

 are of three classes, of which we shall give a brief account 

 in order to show the advantages of the new invention, due 

 to the ingenuity of a young Genevese physicist, M. Raoul 

 Pictet. 



The first class comprises the Ammoniacal Machines. 

 These are based on the principle, applied by M. Carrd, of 

 the solution of ammonia in water. A saturated solution 

 of ammonia is introduced into a boiler which is heated to 

 140'' or 150° C. The ammonia is disengaged under 

 strong pressure, and is liquefied in a condenser washed by 

 a current of ordinary water. The liquid ammonia flows 

 into the refrigerator, where it is evaporated and it returns 

 into the liquid in a gaseous form. The evapora- 

 tion is the source of the cold, which may be made very 

 intense. 



In order to work an apparatus of this kind, it is neces- 

 sary that the first operation be effected, i.e., the liquefac- 

 tion of the ammonia in the condenser. For this purpose 

 it is necessary that the pressure in the boiler correspond 

 to the tension of ammonia vapour, at the temperature of the 

 water of condensation, 30° C. at least in warm countries. 

 This pressure is raised then to fifteen or eighteen 

 atmospheres, an enormous pressure, liable to great 

 danger. 



Under so great tension the gas traverses cast-iron 

 walls of two centimetres, the joints leak, not being 

 air-tight, and the ammonia rapidly escapes from the 

 apparatus. The alkaline solution must then be constantly 

 renewed^ which is very costly. There is another incon- 

 venience. The fire under the boiler causes deposits, 

 which, increasing day by day, give rise to the danger of 

 an explosion. The fear of such a catastrophe demands 

 constant watchfulness. 



In countries less warm, with a water of condensation 

 at 20°, the tension of the ammonia hardly exceeds eight 

 atmospheres. In these circumstances the Carr^ machine 

 works well and produces economical results. But in such 

 countries natural ice is abundant, and the service ren- 

 dered is consequently of less value. 



The second class includes the Ether Machines. Sul- 

 phuric ether was first employed for the manufacture of ice 

 in England. A large pneumatic pump draws up the 

 vapours of ether, which are formed in a tubular refrige- 

 rator, and compresses these vapours in a condenser 

 bathed in spring water. The evaporation may also freeze 

 the water contained in the tanks, while the compression 

 of the vapours and their condensation in the condenser 

 transfer to the spring-water all the heat freed from the 

 water in the tanks, transformed into ice. A pipe allows 

 the condensed ether to return to the refrigerator, and be 

 again subjected to volatilisation. 



These machines, more simple than the anmionia ones, 

 are, however, less workable. Ether is a liquid of small 

 volatility, and gives only weak tensions. At — 4° or — 5° C, 

 this tension varies from 4 to 8 centimetres of mercury 

 according to the quality of the ether. The cylinder of the 

 pneumatic machine must then be of considerable dimen- 

 sions in order to draw up a small weight of ether and 

 produce a limited amount of cold. The whole of the first 

 half of the machine works with an almost complete 

 vacuum, but if the joints, the walls of the tubes, and the 

 caulking of the cylinder are not perfectly hermetic, atmo- 

 spheric air will enter the apparatus ; and should the ma- 

 nometer show that it is present to the extent of one or 

 two centimetres, the evaporisation of the etherj wiU be 

 arrested. With the smallest amount of air present the 

 machine becomes unworkable ; a hole no larger than a 

 pin-point is sufficient to paralyse the half of its normal 

 product. 



Another inconvenience arises from the fact that ether 



is not a body perfectly constant in its chemical charac- 

 teristics. Under the action of frequent changes of con- 

 dition, of frequent volatilisations and condensations, it 

 becomes acidified and transformed into less volatile 

 isomeric bodies. On this account it is necessary fre- 

 quently to change the active liquid, which is very 

 troublesome and expensive. 



Lastly, the greases with which the piston of the cylin- 

 der is lubricated form a close mixture with the ether, a 

 mixture which is carried into all the apparatus, and which 

 also tends to trammel its regular working. 



The third kind, Compressed Air Machine, is the least 

 workable of all, and has invariably failed on trial. Its 

 principle is as follows : — Air is compressed in a large 

 cylinder to nearly three atmospheres. This compression 

 raises the temperature of the air to about 1 50° C. A current 

 of water cools this air, which enters cold into a second 

 cylinder, where it expands from three atmospheres to the 

 ordinary pressure. This work which it produces upon a 

 second piston is equal to the deduction of the original 

 work, for the two cylinders are joined en suite, and are 

 worked by the same rod. The air which is expanded 

 lowers the temperature, and gives the second cylinder 

 about 60° of cold. This air may be utilised to manu- 

 facture ice, or to cool cellars, apartments, &c. 



This machine, in order to work well, requires large 

 cylinders and close-fitting pistons with very little fric- 

 tion, a perfectly regulated introduction into the ex- 

 pansion cylinder, and orifices, valves, and flaps without 

 a flaw. But these conditions are almost impossible to 

 realise in practice. A piston of large size, travelling in 

 a cylinder under a temperature from — 50° to - 60° C, is 

 an abundant source of friction, for it is only imperfectly 

 lubricated by glycerine. A thick coating, produced by 

 the solidification of the vapour of water in the expansion 

 cylinder, is also a cause of accident and trouble in the 

 working. Lastly, the smallest derangement in the aspi- 

 rating or compressing valves of the first cylinder puts an 

 entire stop to the production of cold. These machines, 

 therefore, are absolutely unequal to the practical solution 

 of the problem. 



A machine capable of easily performing the work must 

 comply with the following five essential conditions : — i. Too 

 great pressure must not occur in any part of the appa- 

 ratus. 2. The volatile liquid employed ought to be so 

 volatile that there will be no danger of air entering ; i.e., 

 the pressure must be at least one atmosphere in order to be 

 in equilibrium with the external pressure. 3. It is necessary 

 to have a system of compression which does not require 

 the constant introduction of grease or of foreign materials 

 into the machine. 4. The liquid must be stable, it must 

 not decompose by the frequent changes of condition, and 

 it must not exert chemical action on the metals of which 

 the apparatus is constructed. 5. Lastly, it is necessary, 

 as far as possible, to remove all danger of explosion and 

 of fire, and for this reason the liquid must not be com- 

 bustible. 



If we examine the series of liquids investigated by M. 

 Regnault, only one will be found to satisfy these essential 

 desiderata ; this liquid is sulphurous anhydride, SO2. 



In fact, this body is liquid under the atmospheric "pres- 

 sure at a temperature of - 10° C, and it does not give 

 pressures higher than four atmospheres at a temperature 

 of 35°. This liquid does not act on metals or fats ; it is 

 not combustible, and is the least expensive of aU Imown 

 volatile liquids. By the process of manufacture dis- 

 covered by M. R. Pictet, it costs less than sulphuric 

 ether. 



Thus, by taking advantage of the general principle of 

 the evaporation of a volatile liquid to produce cold, and 

 utilising sulphurous acid, we can obtain a machine which 

 gives results constant in every country, and which acts in 

 a perfectly mechanical and normal manner in all lati- 

 tudes. The following is a brief description of a typical 



