ALKALIMETRY. 467 



canted from the tube into the alkalimeter to be graduated, and 

 a scratch made upon the latter at the mercury surface : this is 

 5 of the ten-grain water measures. Another measure is added 

 and its height marked ; and the same repeated till 20 measures 

 of mercury in all have been added, which are 100 ten-grain water 

 measures. The subdivision of each of these measures into 5 is 

 best made by the eye, and is also marked on the alkalimeter. 

 The divisions are lastly numbered, 0, 5, 10, &c., counting 

 from above downwards, and terminating with 100 on the sole 

 of the instrument. Several alkalimeters may be graduated at 

 the same time, with little more trouble than one, the measured 

 quantities of mercury being transferred from one to the others 

 in succession. The French alkalimeter, d of figure 47, is a more 

 convenient instrument to pour from, but it is too fragile for 

 common use. 



(2) To form the test acid, 4 ounces avoirdupois of oil of 

 vitriol are diluted with 20 ounces of water ; or larger quantities 

 of acid and water are mixed in these proportions. About |ths 

 of an ounce of bicarbonate of soda is heated strongly by a lamp 

 for a few minutes, to obtain pure carbonate of soda ; of which 

 171 grains are immediately weighed; that quantity, or more 

 properly 170.6 grains, containing 100 grains of soda. This 

 portion of carbonate of soda is dissolved in 4 or 5 ounces of 

 hot water; and the alkalimeter filled up to 0, with the dilute 

 acid. The acid is poured gradually into the soda solution, till 

 the action of the latter upon test-paper ceases to be alkaline, 

 and becomes distinctly acid, and the measures of acid necessary 

 to produce that change accurately observed. It may probably 

 require about 90 measures. But it is convenient to have the acid 

 exactly of the strength at which ICO measures of it saturate 100 

 grains of soda. A plain cylindrical jar c, of which the capacity 

 is about a pint and a half is graduated into 100 parts, each con- 

 taining 100 grain measures of water, or ten times as much as the 

 divisions of the alkalimeter. The divisions of this jar, however, 

 are numbered from the bottom upwards, as is usual in mea- 

 sures of capacity. This jar is filled up with the dilute acid to 

 the extent of 90, or whatever number of the alkalimeter divi- 

 sions of acid were found to neutralise 100 grains of soda; and 

 water is added to make up the acid liquid to 100 measures. 

 Such is the test acid, of which 100 alkalimeter measures neu- 

 tralise, and are equivalent to 100 grains of soda; or 1 measure 



