INDUSTRIAL PROGRESS DURING THE YEAR 1875. l v 



Indeed, it may be said that two bodies not absolutely iden- 

 tical never exhibit strictly the same physical or chemical 

 reactions, however closely they may in certain particulars 

 resemble each other. 



Pfaundler confirms the unequal solubility of different faces 

 of the same crystal, remarked by Lecoq de Boisbaudran, and 

 calls attention to his theoretical explanation of it, first pub- 

 lished in 1869. He concludes that those faces of a crystal 

 which possess favorable conditions for resisting the impact 

 of the moving molecules are preserved and grow at the ex- 

 pense of the others. " Thus," he says, " the principle laid 

 down by Darwin is applicable also in the world of molecules. 

 Those forms and combinations which possess the most favor- 

 able conditions of existence are the ones which are preserved." 



Boisbaudran has also shown that very low temperatures 

 may be produced by means of the ammonia ice-machine of 

 Carre by taking suitable precautions. If during the cooling 

 the heater be surrounded with ice-water, or, still better, with 

 a freezing-mixture, it is possible to obtain, even with a ma- 

 chine holding only half a liter, the rapid solidification of sev- 

 eral kilogrammes of mercury. After the freezing of nearly 

 five kilogrammes of this metal in a solid cylinder, the tem- 

 perature within was found to be 48. If ice and salt be 

 added to the water in which the condenser is placed during 

 the heating, it is not necessary to raise the temperature of 

 the heater so high by ten or fifteen degrees. 



Guthrie has given a curious paper upon hydrates (or hy- 

 drated salts) formed at a low temperature, which he calls 

 cryohydrates. He shows, contrary to the generally received 

 opinion, that the minimum temperature attainable by mixing 

 ice with a salt is very independent of the ratio of the two, 

 and of their temperature, and of the state of division of the 

 ice. The temperature of a mixture of ice and a salt is as 

 constant and precise as the melting-point of ice. He ob- 

 serves that the cryohydrates of the nine salts which potas- 

 sium, sodium, and ammonium severallv form with chlorine, 

 bromine, and iodine, are formed at temperatures ranging from 

 28 to 11. Thirty-five salts were examined in this way, 

 and it was found that the temperature at which the cryo- 

 hydrate is formed is precisely that obtained by mixing the 

 given salt with ice. In a subsequent paper he gives addi- 



