20 ACIDIMETRY 



sulphuric acid examined contained that quantity per cent, of pure oil of vitriol, 

 representing 24'4 per cent, of pure anhydrous sulphuric acid : thus 



Divisions. Oil of Vitriol 



100 : 49 :: ei : x = 29-89. 



Anhydrous Acid. 



100 : 40 :: 61 : z = 24-4. 



The specific gravity of an acid of that strength is 1'2178. 



In the same manner, suppose that 100 grains in weight of hydrochloric acid have 

 required 90 divisions (900 grains' measure) of the acidiineter for their complete neu- 

 tralisation, the equivalent of dry hydrochloric acid gas being 36'5, it is clear that 

 since 90 divisions only of the ammonia test-liquor have been employed, the sample 

 operated upon must have contained per cent, a quantity of acid equal to 33'30 of dry 

 hydrochloric acid gas, in solution, as shown by the proportion : 



Divis. Hydrochloric acid. 

 100 : 36-5 :: 90 : x = 32-85. 



The specific gravity of such a sample would be 1-1646. 



Instead of the ammonia test-liquor just alluded to, it is clear that a solution contain- 

 ing one equivalent of any other base such as, for example, carbonate of soda, or 

 carbonate of potash, caustic lime, &c. may be used for the purpose of neutralising 

 the acid under examination. The quantity of these salts required for saturation will 

 of course indicate the quantity of real acid, and, by calculation, the per-centage thereof 

 in the sample, thus : The equivalent of pure carbonate of soda being 53, and that 

 of carbonate of potash 69, either of these weights will represent one equivalent, and 

 consequently 49 grains of pure oil of vitriol, 36 '5 of dry hydrochloric acid, 60 of 

 crystallised, or 51 of anhydrous acetic acid, and so on. The acidimetrical assay is 

 performed as follows : 



If with carbonate of soda, take 530 grains of pure and dry carbonate of soda, 

 obtained by igniting the bicarbonate of that base (see AXKAXIMETRY), and dissolve 

 them in 10,000 water-grains' measure (1,000 acidimetrical divisions) of distilled water. 

 It is evident that each acidimeter full (100 divisions) of such a solution will then 

 correspond to one equivalent of any acid, and accordingly if the test-liquor of car- 

 bonate of soda be poured from the acidimeter into a weighed quantity of any acid, 

 with the same precautions as before, until the neutralisation is complete, the number 

 of divisions employed in the operation will, by a simple rule of proportion, indicate 

 the quantity of acid present in the sample as before. Pure carbonate of soda is easily 

 obtained by recrystallising once or twice the crystals of carbonate of soda of com- 

 merce, and carefully washing them. By heating them gradually they melt, and at a 

 very low red heat entirely lose their water of crystallisation and become converted 

 into pulverulent anhydrous neutral carbonate of soda, which should bo kept in well- 

 closed bottles. 



When carbonate of potash is used, then, since the equivalent of carbonate of potash 

 is 69, the operator should dissolve 690 grains of it in the 10,000 grains of pure dis- 

 tilled water, and the acidimeter being now filled with this test-liquor, the assay is 

 carried on again precisely in the same manner as before. Neutral carbonate of potash 

 for acidimetrical use is prepared by heating the bicarbonate of that base to redness, 

 in order to expel one equivalent of its carbonic acid ; the residue left is pure neutral 

 carbonate of potash ; and in order to prevent its absorbing moisture, it should be put, 

 whilst still hot, on a slab placed over concentrated sulphuric acid, or chloride of cal- 

 cium, under a glass bell, and, when sufficiently cool to be handled, transferred to bottles 

 carefully closed. 



To adapt the above methods to the French weights and measures, now used also 

 generally by the German chemist, we need only substitute 100 decigrammes for 100 

 grains, and proceed with the graduations as already described. 



A solution of caustic lime in cane sugar has likewise been proposed by M. Peligot 

 for acidimetrical purposes. To prepare such a solution, take pure caustic lime, ob- 

 tained by heating Carrara marble with charcoal in a furnace ; when sufficiently 

 roasted to convert it into quicklime, slake it with water, and pour upon the slaked 

 lime as much water as is necessary to produce a milky liquor ; put this milky liquor 

 in a bottle, and add thereto, in the cold, a certain quantity of pulverised sugar-candy ; 

 close the bottle with a good cork, and shake the whole mass well. After a certain 

 time it will be observed that the milky liquid has become very much clearer, and 

 perhaps quite limpid ; filter it, and the filtrate will be found to contain about 50 parts 

 of lime for every 100 of sugar employed. Tho liquor should not be heated, because 

 caccharate of lime is much more soluble in cold than in hot water, and if heat were 



