* 
Researches on Salts. 343 
not found a phosphate which does not retain some water at a 
pretty, high temperature. — 
The _ pyrophosphates have afforded me similar facts. Thus 
e pyrophosphate of barytes was found to consist of ; 
PO? (Ba? H*?)=P?* O°, 2Ba? O, 2H? O. 
“ee 
- Tam well aware that it may be objected that the temperature 
‘at which the water of constitution is expelled, is higher or lower 
according to the salts; this objection is based on the reactions. 
ut have I not shown above that the composition of the precipi- 
tated salts can vary according to certain conditions of mass and 
temperature? It is not then exact to say that any salt, for exam- 
ple a tribasic, will always give, by double decomposition, precip- 
itates of an analogous composition, i.e. tribasic. The principle 
based by Mr. Graham on two or three facts, is in contradiction to 
fifty others. Water, in which all these reactions take place, m 
ifies them continually, and determines metamorphoses in mineral » 
bibasic pyrophosphates and tribasic chaplains why not est 
the same differences in the nitrates, the sulphates, the chlori r 
nomena, when subjected to heat, from the nitrates of K, Na, b, 
Ba? The first always retain the elements of water, and give on 
g, nitric acid, as well asa subnitrate retaining in its turn 
the elements of water, and the same is true of the whole Debs, 
sian series [NO,(MH,)]|; while the nitrates of K, Na, 
are anhydrous, and produce under the same circumstances, n trites 
and oxygen gas 
I will mention another fact not less conclusive. Alum) which 
chemists consider as a combination of two neutral salts, has 
acid reaction. At 248° F.. it loses five-sixths of its water, at 
then becomes 
50:,K* 0,8? O. 
SO r ey al) H*)= $380, Al‘ 03, 3H? O, 
This product is easily redissolved in water. But let it 
at 392° F’. and it loses all its water and becomes insoluble. 
have produced this site insoluble alum in the wet way: 
necessary is to sprinkle the vl . ase with concen 
sulpavitic acid, and app i few minute 
crystals will be changed j a ‘ergtaline nah insoluble on 
: in it rapidly. However, if this insol- 
er eight or ten days, it may be seen 
changing by degrees into small octahedrons of soluble alum. 
