466 



SODIUM. 



phate of soda, and often insoluble matter, and varies consider- 

 ably in value. The soda in combination with carbonic acid 

 only, is available in the application of the salt as an alkaline 

 substance. The pure anhydrous carbonate of soda consists of 

 58.58 soda and 41.42 carbonic acid, but the best soda-salts of 

 commerce rarely contain so much as 50 per cent, of available 

 soda. The operation of ascertaining the proportion of alkali in 

 these salts, and in other forms of the carbonate of soda, is a pro- 

 cess of importance from its frequent occurrence, and interesting 

 as a method of analysis of easy execution and applicable to a 

 great variety of substances. I shall therefore describe minutely 

 the mode of conducting it. 



ALKALIMETRY. 



The experiment is to find how many measures of a diluted 

 acid are required to destroy the alkaline reaction of, and to 

 neutralise 100 grains of a specimen of soda-salt. (1) The acid is 

 measured in the alkalimeter, which is a straight glass tube, or 

 FIG. 47. very narrow jar with a lip, about 



5-8ths. of an inch in width, and 

 14 inches in height, mounted 

 upon a foot, as a of figure 47, 

 capable of containing at least 

 1000 grains of water. It is 

 graduated into 100 parts, each 

 of which holds ten grains of 

 water. In the operation of di- 

 viding such an instrument it is 

 more convenient to use mea- 

 sures of mercury than water; 

 135.68 grains of mercury, being 

 in bulk equal to 10 grains of water, 678.40 grains will be equal 

 to 50 grains of water. A unit measure may be formed of a 

 pipette, b in figure 47, made to hold the last quantity of mer- 

 cury, into which the metal is poured, the opening at the 

 point of the pipette being closed by the finger, and the height 

 of the mercury in the tube marked by a scratch on the glass, 

 made by a triangular file. The bulk of twice that quantity of 

 mercury, or 100 water grain measures, may likewise be marked 

 upon the tube. The former quantity of mercury is then de- 



