= on 
s ’ 344 ~~ Researches on Nalis. 
From this it seems to me that alum contains, as truly as 
phosphates, water of constitution, which when expelled from, @ 
salts, leaves it a body altogether different. 
I would also call to mind that the tion ee 
minium is a body volatile without decomposition, while the crys- 
tallized Aydrochlorate of alumina is decomposed by heat int 
hydrochlorie acid and pure alum 
The conclusions which follow ican ok nee I have instanced, f 
may be summed up in the following man 
he expressions neutral salt, basic salt, wer salt, are arbitrary 
terms, used to designate particular types of salts which differ 
from each other by the elements of H? O, or of the metallic 
oxyd M? 0. 
These types are peereuerabls, with greater or less facility, 
according to certain conditions of mass, of temperature, etc., 
it is impossible to daneries with precision in the present 
of the science; and there are absolutely the same chemical 
between the metaphosphates, the pis sao ao and 
na a inge as between the nitrates and the basic 
or of a metallic oxyd, and then give rise toa new t 
ere is no rule for predicting these modification 
fo'make my idea more intelligible, I will sweita out a i 
Genus Puospuate, POZ(M?)+M? 0. 
A. Sub-genus eererer sate 
POi (M?)—3 M? O= =PO* (M)=[P*O*, M* OO} a2 
All the so-called metaphoaphates will belong to this typer 
B. Sub-genus equiphosphate, | PO(M?)=[P? O+,2M? O]. 
it includes a few Pyrophospunes, and especially the — of 
Ea 212° F.,. POj (Na? ). 
sai take this occasion to i that, the cubical alum has exactly the same 
composition as the alum in octahedr The formation of cubical alum or Ro- 
man alum belongs to the class of bene omena ~ crystallization so eet investiga- 
by M. Beudant. I shall give in my wo the proofs respecting it. 
M. Jacquelain (Comptes Rendus de ['Acad., -. xxiv, p. 44) affirms that alum 
contains 22 atoms of water instead of 24 in the usual formula. This assertion 18 
not sige at te: the new formula would require 43- per cent. of water, and we 
ee er cent. 
pasta nbical al gen percent. Now this is exactly the 
