474 ANALYSIS OF THE 



for its decomposition 23.1 of real sulphate of soda; and the 

 products of this decomposition are 22.1 of real sulphate of 

 lime, and 19 of muriate of soda *. The former of these pro- 

 ducts being collected and dried, may be weighed, and the lat- 

 ter being deducted from the whole quantity of muriate of soda 

 obtained by evaporation, the remainder will be the quantity 

 originally contained in the water. The obtaining these quan- 

 tities, therefore, or near approximations to them, will be at 

 once a confirmation of the preceding analysis, and of the accu- 

 racy of these proportions. 



A pint of the water was evaporated to about one-fourth ; the 

 quantity of real sulphate of soda required for the decomposi- 

 tion of its muriate of lime, it has been just stated, is 23.1 

 grains. But, by previous trials, I had found, that a small ex- 

 cess of sulphate of soda renders the decomposition more com- 

 plete ; 24 .grains, obtained by exposing crystallised sulphate 

 of soda to a red heat, were, therefore, added. The liquor soon 

 became turbid and thick. I had also found, that to render the 

 decomposition more complete, it is of advantage not to evapo- 

 rate at once to dryness, but to add small quantities of water 

 occasionally for some time during the boiling. The experi- 

 ment having been conducted in this manner, a precipitate of 

 sulphate of lime was collected, which, when washed and dried, 

 weighed 19 grains. The liquor being evaporated, afforded of 

 dry salt 51.6 grains. But on dissolving this salt in water, a 

 deposite of sulphate of lime remained undissolved ; and even 

 on again evaporating to dryness, and re-dissolving in water, a 

 small portion was deposited for three successive times. The 



whole 



* The inspection of the scale of chemical equivalents, gives at once these 

 numbers; and this highly useful instrument, lately invented by Dr Wollaston, 

 facilitates greatly all such researches, by the number of results it presents with- 

 out the necessity of calculation. 



