466 



Messrs. Playfair and Joule on 



Pyrophosphate of soda, vol. in solution 89*6 



90-4 

 Mean . . 90-0 

 On immersing 56'04/ grains of the salt in a saturated solu- 

 tion, an increase of 30*5 was obtained in two experiments. 



Sp. gr. 

 Pyrophosphate of soda, vol. of salt 122-0 ... 1*836 



By tabulating the results thus obtained we find the follow- 

 ing relationship between the class of alums. 



Table III. — Showing the volumes of certain Alums*. 



Designation. 



Nanje. 



Formula. 



Atomic 

 weight. 



Volume in solution. 







Volume in stat« of «alt. 



la 



3"« 



-a b 



^■w 



Potash alum ... 

 Ammonia alum. 

 Chrome alum... 



...{ 



Iron alum 



Pyrophosphate \ 

 of Soda ...J 



JAlaOs.SSOj.KO.SOal 

 \ ■ +24HO J 



/AI2O3.3SO3+NH4OI 

 1 SO3+24HO J 

 rCrA.SSOa + KO.l 

 I SO34-24HO J 

 FejOg, 3S63+NH4O, 1 

 SO3+24IIO / 



2NaO,PO5+10HO 



474-95 



454-26 



5041 



48103 



22415 



2177 

 2271 



215-8 

 228 

 90 



24 

 25 

 24 

 25 

 10 



216 

 225 

 216 

 225 

 90 



275-2 

 279-6 

 2760 

 2800 

 122 



275 

 275 

 275 

 275 

 121 



1-727 

 1-652 

 1-833 

 1-749 

 1-852 



1-726 

 1-625 

 1-826 

 1-718 

 1-836 



The peculiarity of the salts described in the above table is, 

 that the quotient of the divisor for the potash alums in the 

 solid state is not the same as in the state of solutionj and that 

 the ammoniacal alums possess one volume in solution greater 

 than the corresponding potash alums, both of which peculi- 

 arities will find an explanation as we proceed. Pyrophos- 

 phate of soda shares this peculiarity, and is therefore intro- 

 duced into the table. 



We now proceed to describe a class of hydrated salts, 

 in which the divisor for the solid volume is certainly not the 

 number 11. 



Carbonate of Soda, NaO, CO2+ 10HO= 143-4.— On dis- 

 solving 35-85 grains of this salt in 1000 grains of water, the 

 increase was 22-5 in one experiment at 64% and 22-9 in a 

 second experiment at 65°. 



I. NaO, CO2 + lOHO, vol. in solution 90-0 



r II 9V6 



Mean . . 90*8 

 * Vidf conclusion for explanation of the high volume of ammonia alums. 



