1874.] 



Carbonic Acid by Saline Solutions. 



193 



receiver. To the tubulure was attached a bulbed U-tube, and, by 

 means of an aspirator, air could be constantly sucked through. The 

 carbonic acid coming off was retained by baryta-water of known strength 

 distributed between the receiver and the U-tube ; what remained unneu- 

 tralized was determined by oxalic acid, the point of neutralization being 

 indicated by rosolic acid. The oxalic acid was rather stronger than 

 tenth normal; it contained 6-478 grammes C 2 H 2 O 4 +2H 2 O in the 

 litre. One litre baryta-water required 3235 cub. centims. oxalic acid for 

 neutralization. 



The method of conducting the operation was as follows : Carbonic acid 

 was passed through the solution until it could be assumed to be satu- 

 rated. The object being to determine the carbonic acid retained by the 

 salt, it was necessary to get rid, as much as possible, of the simply dis- 

 solved gas. This was effected by drawing six or seven litres of air 

 through the solution cold, then heating it to boiling, and allowing it to 

 boil for a couple of minutes in a current of air. The receiver, with the 

 baryta solution, was then attached, and the distillation continued in a 

 current of air, until the contents of the flask were nearly dry. The 

 amount of carbonic acid was given by the remaining alkalinity of the 

 baryta-water. 



Experiments on sulphate-of-magnesia solution, containing 12'3 

 grammes crystallized salt per litre. As all were conducted in precisely 

 the same way, it will be sufficient to give the results in a tabular form. 

 The first three experiments were made with one and the same solution ; 

 for the last two a fresh solution, prepared, to all appearance, in exactly 

 the same way as the previous one, was used. The difference in the results 

 shows the precarious nature of the combination. 



Two experiments were made with a solution prepared as follows : 

 The quantity of sulphuric acid necessary for the formation of 12'3 

 grammes crystallized sulphate of magnesia was diluted to a litre, and pul- 

 verized carbonate of magnesia suspended in it. Although the mixture 

 was allowed to stand over night, shut off from the influence of the 

 atmosphere, the solution was still very acid. It is well known that car- 

 bonate of magnesia is difficultly soluble in cold dilute acids. To have 

 heated the solution would have frustrated the object of the experiment, 

 which was, by bringing nascent sulphate of magnesia together with 



