Mr. Graham on the Heat disengaged in Combinations. 413 



in half an equivalent of chloride of ammonium at 63°, the fall 

 was 0°*45, 0°*45, 0°*47 F., of which the mean is 0°*46 F. 

 The disengagement of heat in the formation of this second 

 double salt is therefore 0°*60-0°*46 = 0°*14 F. It is doubt- 

 ful whether the heat here can be ascribed to hydration ; as 

 the resulting double salt has been crystallized at the usual 

 temperature by Dr. Kane, both anhydrous and with one atom 

 of water. The circumstance however of the chloride of mer- 

 cury being dissolved by a solution of sal-ammoniac in much 

 larger quantity than by pure water, affords a proof of the im- 

 mediate formation of a double salt on the solution of its con- 

 stituents together, which cannot be obtained in the magne- 

 sian or aluminous double sulphates. 



I may be allowed to place under the present head of sul- 

 phuric acid, the results of experiments on the solution in water 

 of two double sulphates, namely sulphate of zinc and soda, 

 and sulphate of manganese and soda, no experiment on a 

 double salt of the soda division of this class being recorded 

 in the former paper. The sidphate of zinc and soda, formed 

 by Mr. Arrott, was in excellent crystals, containing four atoms 

 of water ; of which the composition is expressed by the for- 

 mula ZnO, S0 3 + NaO, S0 3 + 4 HO. One-half of an equi- 

 valent, 58*61 grains of the salt, containing 11*25 grains of 

 water of crystallization, was dissolved in 988*8 grains of water 

 at 62° F., with a fall in three experiments of 0°*02 R., 0°*04, 

 0°*02 ; mean 0°*03 R. 



Of the same salt made anhydrous by heat and fused, half 

 an equivalent, or 47*41 grains, was dissolved in 1000 grains 

 of water at 62° F., with a rise in three experiments of 1°*86, 

 1°'87, 1°*84; mean 1°*86 R. Doubling the results of the ex- 

 periments in both cases, to obtain the changes for a whole 

 equivalent, we find — 



Cold on solution of ZnO, S0 3 + NaO, SO3 + 4HO 0°*06 R. 

 Heat on solution of ZnO, S0 3 + NaO, SO s 3°'72 R. 



As the two sulphates, in all the double sulphates of this class 

 containing sulphate of soda, crystallize apart when the salt 

 is dissolved in water at 62°, the double salt is probably de- 

 composed in these experiments ; and the circumstances of its 

 solution may therefore be very different from those of a mag- 

 nesian double sulphate containing sulphate of potash. 



The sulphate of manganese and soda, for which I am also 

 indebted to Mr Arrott, was in good crystals containing two 

 atoms of water; the formula of this salt being MnO, S0 3 + 

 NaO, S0 3 + 2 HO. 1 equivalent of the crystallized salt, 

 103*2 grains, containing 11*25 grains of water of crystalliza- 



