CATARACTS, AND INUNDATIONS. 189 



the presence of this acid, he directs its tincture in water to be used, 

 sufficiently diluted, till it has a blue colour. He absolutely rejects 

 syrup of violets, because it is subject to ferment, and because it is 

 scarcely ever obtained without adulteration in Sweden. Morveau 

 adds in a note , that it is easy to distinguish a syrup coloured by 

 turnsole, by the application of corrosive sublimate, which gives it a 

 red colour, while it converts the true syrup of violets to a green. 



Lime-water is one of the most useful agents in the analysis of 

 mineral waters, though few chemists have expressly mentioned it in 

 their works. This fluid decomposes metallic salts, especially sulphat 

 of iron, whose metallic oxyde it precipitates ; it sepa'rates alumine 

 and magnesia from the sulphuric and muriatic acids, to which these 

 substances are frequently united in waters. It likewise indicate* 

 the presence of carbonic acid, by its precipitation. M. Gioanetli, 

 a physician of Turin, lias very ingeniously applied it to ascertain 

 the quantity of carbonic acid contained in the water of St. Vincent. 

 This chemist, after having observed that the volume or bulk of 

 this acid, from which its quantity has always ben estimated, must 

 van. according to the temperature of the atmosphere, mixed nine 

 parts of lime-water with two parts of the water of St. Vincent: he 

 weighed the calcareous earth formed by the combination of the 

 carbonic acid of the mineral water witji lime, and found, according 

 to the calculation of Jurmin, who proves the existence of thirteen 

 ounces of this acid in thirty-two ounces of chalk, ihttt the water of 

 St. Vincent contained somewhat more than fifteen grains. But as 

 the lime-water may seize the carbonic acid united with the fixed 

 alkali, as well as that which is at liberty, M. Gioanetti, to ascertain 

 more exactly the quantity of this lust, made the snme e>perimi'nt 

 with water deprived of its disengaged acid by ebullition. This 

 process may therefore be employed to determine, in an easy and 

 accurate manner, the weight of disengaged caibonic acid, con- 

 tained in a gaseous mineral water. 



One of the principal reasons which have induced chemists to 

 consider the action of re. agents in the analysis of mineral waters as 

 very fallacious, is that they are capable of indicating several dif- 

 ferent substances held in solution in waters, and that it is then very 

 difficult to know exactly the effects they will produce. This obser- 

 vation relates more especially to potash, considered as a re-agent, 

 because it decomposes ull the salts which arc formed by the union 



