S26 Prof. H. Rose on the Isomeric Modifications 



the silver salt, as might be expected from the circumstance 

 that on their formation the solutions which are originally 

 neutral acquire an acid reaction, well deserves investigation. 



A salt of silver having an analogous composition can be 

 prepared from Graham's salt. M. Fleitmann decomposed 

 Graham's salt with nitrate of silver, filtered the precipitate 

 immediately, washed it slightly with cold water, and then 

 pressed it strongly between blotting-paper. The water used 

 in the washing possessed a barely acid reaction. The fused 

 compound gave the following per-centage composition :— 



Phosphoric acid . . . 37*62 

 Oxide of silver . . . 61-18 



98-80 



which closely approximates the composition calculated ac- 

 cording to the formula AgO, P^ O^, which requires 61-89 oxide 

 of silver and 38 -11 phosphoric acid. The loss probably arises 

 from its containing a little soda, which was not removed in 

 consequence of the rapidity with which the compound was 

 washed. It is thus evident, that when the silver salt is preci- 

 pitated and separated as quickly as possible from the liquid, 

 it corresponds in composition with Graham's salt; but that, 

 on prolonged contact with the liquid, even when cold, it be- 

 comes decomposed and loses acid. 



Whether anything similar occurs in the case of the other 

 precipitates has not been determined ; but it is not improbable, 

 as at first they are precipitated in a pulverulent form, and only 

 acquire the oily appearance when powerfully shaken, by which 

 they probably lose a portion of the phosphoric acid. 



2. The acid existing in those remarkable salts which Fleit- 

 mann and Henneberg obtained from the acid phosphate of 

 soda, or rather from the microcosmic salt, by fusion and very 

 gradual cooling*, may be regarded as a second submodifica- 

 tion of metaphosphoric acid. This salt has exactly the same 

 composition as the metaphosphates; it contains the same 

 number of atoms of base and acid, and has therefore the com- 

 position of Graham's salt ; but differs from it in its opacity and 

 crystalline structure, whilst Graham's salt is transparent and 

 amorphous. It crystallizes from its solution with 45 atoms of 

 water, whilst Graham's salt cannot be made to crystallize. Its 

 solution, like that of Graham's salt, exerts a neutral reaction. 



The most remarkable property of the acid of this salt is, 



that it forms with all bases compounds soluble in water, in 



which respect it differs essentially from all the modifications 



of phosphoric acid. The salts, even the silver salt, can be 



* Chem. Gaz., vol. vi. p. 289. 



