474 Messrs. Playfair and Joule on 



water is exactly the same as that of ice itself. Sugar belongs 

 to this category, not because the FIj, Ojj are feebly attached, 

 for it has yet to be shown that they are present quasi water. 

 The fact however that these 1 1 atoms of hydrogen and oxygen 

 take up the same space as liquid water in solution, and as ice 

 in the solid state of sugar, and that the 12 atoms of carbon 

 have ceased to occupy space, is a matter of supreme interest, 

 and cannot fail to lead to important results when we come to 

 the consideration of organic compounds. 



The fourth class in this section finds its representatives in 

 the sulphates of the magnesian class of metals, and perhaps 

 ought to include the magnesian chlorides also. They possess 

 their constitutional water with the usual volume of 11, while 

 the water feebly attached is present with the volume of ice. 



Although, then, we have four distinct groups in the section 

 of salts possessing a large amount of hydrate water, we have 

 only two modifications of volume, the one represented by a 

 number equal or approximating to 11, the other by the vo- 

 lume of ice itself, viz. 9"8. 



We now proceed to the consideration of salts which either 

 are destitute of water, or contain it in small proportion only. 

 The volumes affected by them must be volumes peculiar to 

 themselves, and not, as in the present section, to the water 

 with which they are combined. 



Section II. 



Sulphates with a small proportion of Water of Hydration, 

 Anhydrous and Double Sulphates. 



Sulphate of Potash, KG, SO3 ^ 87-25.— Half an equi- 

 valent of this salt, dissolved in 3140 grains of water of 37°, 

 increased 7*2, and at 80°, 9*0; the same quantity dissolved 

 in 1000 grains of water at 66°, increased 90. 



I. II. KO, SO3, vol. in solution 18-0 



A whole equivalent of the salt being placed in its saturated 

 solution effected a rise in the stem of 33*0 at a temperature of 

 55°; and a repetition of the experiment gave the increase 



33-1. 



Sp. gr. 



I. KO, SOg, vol. ofsall 33-0 ... 2-644 

 II. ... ' ... 33-1 ... 2-636 



Mean . . 33-05 2-640 



Sulphate of Potash and Sidphate of Water, KO, 803+ HO, 

 SO3 = 13635. — The fourth of an equivalent (34-08 grains), 

 being dissolved in 1000 grains of water, caused an increase of 



