232 M. Debray on some Crystallized Phosphates and Arseniates. 



But in the present state of science it would be difficult to admit 

 this explanation. 



" 2. In the inside the gases are at rest ; outside, hydrogen is in 

 motion. If it were to this difference alone that the phenomenon 

 had to be attributed, I might draw important conclusions in 

 support of the mechanical theory of heat, of the new ideas on 

 the constitution of gases, and of the hypothesis of Mr. Graham. 

 But before this I desire to examine carefully the conditions of 

 the experiment, which might have escaped me, and discuss them 

 again in all their parts/'' 



M. Debray has made a communication on the production of 

 some crystallized phosphates and arseniates*. The phosphates 

 and arseniates obtained by precipitating metallic solutions by 

 soluble phosphates are gelatinous, or at least amorphous ; but 

 the precipitates formed in solutions of magnesia or cobalt by 

 phosphate of ammonia are rapidly transformed into small crystals 

 of definite composition. Debray finds now that this transforma- 

 tion of phosphates is more general than had been supposed, and 

 that there are few which do not finally pass, under favourable 

 circumstances, from the amorphous state into that of well- 

 defined crystals. He explains this as follows. The amorphous 

 precipitates produced by soluble phosphates and metallic solu- 

 tions are not quite insoluble in the saline, acid, or alkaline liquors 

 in which they are formed. Hence if by any diminution of tem- 

 perature their solubility diminishes, a portion crystallizes either 

 on the sides of the glass or on the amorphous substance ; an 

 increase, on the contrary, dissolves a part of the amorphous sub- 

 stance, which is more readily soluble than the crystals; so that 

 by a series of changes in the solvent power of the liquid, as 

 feeble as may be desired, but continuous, the amorphous sub- 

 stance ought to be entirely changed into crystals. 



This transport of matter from the amorphous to the crystal- 

 line state is analogous to the phenomena discovered by M. 

 Devillet, in which amorphous oxides were converted into crystal- 

 line oxides under the influence of a current of hydrochloric acid. 

 Here the acid acting on the amorphous oxide gives a chloride and 

 water, between which the inverse action takes place. But the 

 oxide thus formed is crystalline, and much more difficult of 

 attack than the amorphous, which is thus acted upon until it is 

 entirely changed. 



M. Debray describes the production of a series of oxides be- 

 longing to the magnesian group. At the ordinary temperature 

 he obtains with an excess of phosphate, in two or three days, 



* Comptes Rend us, July 4, 1864. 

 t Phil. Mag. vol. xxii. p. 515. 



