]194 DB' K,' ANGUS SMITH 



a weak solution is sufficient. The strength used is given ; 

 hut the precipitate does not differ when the water is stronger^ 

 If, however, the water should he extremely weak, several 

 times weaker than the ahove, there is a difference, The 

 carhonate of haryta dissolves in the water to a very per- 

 ceptible extent. The first precipitate made in baryta-water 

 by oxalic acid also, although very white at the surface 

 where there is much acid and before mixing, disappears on 

 shaking to a perfectly transparent and brilliant liquid. I 

 speak, however, of very weak solutions; a solution five 

 times weaker than the one given as an example, would be 

 incorrect on account of its weakness. 



Hitherto baryta has been spoken of; and it may well be 

 asked why lime should not be preferred. The same pre- 

 cipitate to all appearance may be got with lime-water. 

 Tables III. and IV. are constructed for lime-water, on 

 exactly the same principles as the former ones. It will be 

 seen that lime is so soluble or so transparent that it requires 

 three times as much space or air from which to collect its 

 equivalent of carbonic acid needful to produce the required 

 opacity. This is, of course, an objection. Still, lime is to, 

 be had everywhere, and lime-water has not the poisonous 

 properties ascribed to baryta-water. 



