DISTILLATION. 269 



The carbonate of potash has likewise been employed as a 

 test, from its dissolving with more or less ease according to 

 the quantity of water contained in the alcohol. 



In the year 1770, the Spanish government ordered oil to 

 be made use of as a test ; the process consisted in letting a 

 drop of oil fall upon the alcohol ; the strength of the li- 

 quor was determined by the depth to which the oil sunk 

 in it. It is evident that this method is very inexact, as the 

 depth to which the oil will sink must depend much upon the 

 size of the drop, and the height from which it is allowed to 

 fall. 



In the year 1772, Messrs, Borie and Pouget arrived at 

 some conclusions, which ended in giving to commerce a hy- 

 drometer of a sufficient degree of -precision to prevent errors 

 of much consequence in estimating the specific gravity of 

 alcohol. 



After having made some very exact experiments upon mix- 

 tures of pure alcohol with water, and upon the effect of tem- 

 perature at all possible degrees of concentration, these two 

 learned philosophers adopted an instrument which allows for 

 the variations of temperature. This hydrometer has con- 

 tributed not a little towards raising the reputation of south- 

 ern brandy in the north, by furnishing it to commerce of its 

 full strength. 



So necessary is the use of a good hydrometer in commerce, 

 that I have seen for more than five years our Languedoc 

 merchants buying Spanish brandy, of which the strength was 

 not uniform, and confining themselves to rendering it of the 

 degree suitable for being sent into the north, and all the 

 other countries where it is consumed. 



In the south, where the greater part of the brandy distrib- 

 uted in commerce is manufactured, it is known under differ- 

 ent names, which are given to various degrees of rectifica- 

 tion. That which marks from 20° to 22° {=z specific gravi- 

 ty of 0,9a5 to 0.923) is called Holland j^roof. 



This first quality, when more concentrated, and re- 

 duced to § by the subtraction of the water contained in it, 

 takes the name of three Jive. When deprived of ^ or ^ more 

 of its aqueous principle, it is known as three six and three 

 seven. 



At Paris, and elsewhere, the hydrometers of Baum6 or 

 Cartier are employed for ascertaining the grade of alcohol: 

 these instruments are less exact than that of Borie, but are 

 sufficiently so for commercial purposes. 

 23* 



