W Professor Berzelius on Thorina, 



B. OXYSALTS. 



Sulphate of Thorina. — This salt is obtained when thorina, 

 previously heated to redness, is rubbed to fine powder, di- 

 gested with a mixture of equal parts of water and sulphuric 

 acid till all the water is evaporated, and the excess of acid 

 driven oflf by gentler heat. The salt which remains has an 

 earthy appearance. In a large quantity of cold water it dis- 

 solves immediately ; but, if the quantity of water be so small 

 as to cause the development of heat when poured upon the 

 salt, it takes a much longer time to dissolve. The solution, 

 left to spontaneous evaporation at a low temperature, deposits 

 transparent ciystals, and leaves at last a very sour mother 

 liquor^ which contains almost nothing but sulphuric acid, and 

 gives a very slight precipitate when saturated with ammonia. 



The crystallized salt is neutral sulphate of thorina in rhom- 

 boedral crystals. These crystals undergo no change at the 

 common temperature and humidity of the atmosphere, but in 

 very warm and dry air they become milk-white without falling 

 asunder. They contain 29.4 per cent, of water, the oxygen in 

 which is five times that in the earth. When they fall to powder, or 

 are gently heated, they lose three-fifths of this water. The salt, 

 like the sulphate of yttria, dissolves very slowly in water, so 

 that the crystals may be very long in that liquid without losing 

 the sharp edges. In powder it dissolves more easily, and water 

 afterwards takes up a large quantity of it. Thrown into hot 

 water, the crystals lose their transparency, and become milk- 

 white ; and if the water be heated to boiling, they become 

 covered with a white deposit, which dissolves as the water 

 cools. If a much-diluted solution of the salt be heated 

 to boiling, the water becomes opalescent ; but if it be in a flat 

 vessel, and be blown upon, it becomes clear. These phenomena 

 are derived from the property which this salt possesses of losing, 

 at a temperature varying with the degree of concentration of 

 the solution, a portion of its combined water of crystalliza- 

 tion — becoming, from a combination of five, one with only two 

 atoms, and which new combination is exceedingly difficult 

 of solution, and continues so till it again takes up the three 

 other atoms. For this reason it may be washed out, with- 

 out great loss, after the manner already mentioned, with water 



