ALKALIMETRY 



ingly it must bo further diluted with water, to bring it to tho standard strength ; and 

 this may at once be done, in the present instance, by adding 20 measures of water to 

 every 80 measures of the acid. This is best accomplished by pouring the whole of tho 

 acid into a large glass cylinder, divided into 100 equal parts, until it reaches the mark 

 or scratch corresponding to 80 measures ; the rest of tho glass, up to 100, is then filled 

 up with water, so that the same quantity of real acid will now be in the 100 measures 

 as was contained before in 80 measures. 



22. The acid adjusted as just mentioned should be labelled ' Test Sulphuric Acid 

 for Potash,' and kept in well-stoppered bottles, otherwise evaporation taking place 

 would render the remaining bulk more concentrated, consequently richer in acid than 

 it should be, and it would thus, of course, become valueless as a test acid until re- 

 adjusted. Each degree or division of the alkalimeter of such an acid represents 1 

 grain of pure potash. 



23. The alkalimetrical assay of soda is also made with sulphuric acid, in preference 

 to other acids, but it must bo so adjusted that 100 alkalimetrical divisions (1,000 

 water-grains' measure) of acid will exactly neutralise 170'98 of pure anhydrous 

 carbonate of soda, that quantity containing 100 grains of pure soda. 



24. Dissolve, therefore, 171 grains of pure anhydrous neutral carbonate of soda, 

 obtained as indicated before, in five or six ounces of hot water, and prepare in tho 

 meantime the test sulphuric acid, by mixing 1 part, by measure, of ordinary concen- 

 trated sulphuric acid with about 9 parts by measure of water, exactly as described 

 before ; stir the whole thoroughly, let the mixture stand until it has become quite cold, 

 then pour 1,000 water-grains' measure of the dilute acid so prepared into an alkali- 

 meter that is to say, fill that instrument up to 0, taking the under line as the true 

 level, and then, whilst stirring briskly the aqueous solution of the 171 grains of car- 

 bonate of soda with a glass rod, pour the acid, with increased precaution as the satu- 

 rating point is approaching, into the vortex produced, until by testing the liquor 

 alternately with reddened and with blue litmus-paper, or with grey litmus-paper, as 

 before mentioned, the exactly neutralised point is hit 



25. If the whole of the 100 alkalimetrical divisions (1,000 water-grains' measure) 

 have been required to effect the neutralisation, it is a proof that the acid is of the 

 right strength, but if this be not the case, it must be adjusted as described before 

 that is to say : 



26. Suppose, for example, that only 75 alkalimetrical divisions or measures of tho 

 acid in the alkalimeter have been required to neutralise tho 171 grains of neutral 

 carbonate of soda operated upon, then 75 measures of the acid should be poured at 

 once into a glass cylinder accurately divided into 100 parts ; the remaining 26 



divisions should then be filled with water, and the whole being now 

 Btirred up, 100 parts of the liquor will of course contain as much 

 real acid as 75 parts contained before, and accordingly the acid may 

 now be used as a test acid for the alkalimetrical assay of soda, each 

 degree or division of the alkalimeter representing one grain of pure 

 soda. 



27. The stock of test acid should be kept in well-stoppered flasks, 

 that it may not vary in strength by evaporation, and be labelled 

 ' Test Sulphuric Acid for Soda.' 



28. Instead, however, of keeping two kinds of 'test sulphuric 

 acid," of different saturating powers as described, the one for potash, 

 the other for soda, one kind only may bo prepared BO as to serve 

 for both alkalis, by constructing, as is very often done, an alka- 

 limeter adjusted so as to indicate the quantities of the acid of a 

 given strength required for the saturation or neutralisation of both 

 potash or soda, or of their respective carbonates ; and this, in fact, 

 is the alkalimeter most in use in the factory. 



It should be in shape similar to that of Gay-Lussac's (see fig. 22), 

 or that described in figs. 23 and 24; but, like that represented by 

 fig. 21, it generally consists of a tube closed at one end, about three- 

 fourths of an inch internal diameter and about 9i inches in length ; 

 it is graduated into 100 equal parts, and every division is numbered 

 from above downwards (see fig. 30). 



The following directions for their construction are given by Pro- 

 fessor Faraday. 'Let the tube represented in the margin have 1000 

 grains of water weighed into it ; then let the space it occupies bo 

 graduated into 100 equal parts, and every ten divisions numbered 

 from above downwards. At 22'1 parts^or 77'99 parts from the 

 bottom, make an extra line, a little on one side or even on the opposite 

 side of the -graduation, and write at it with a scratching diamond, soda ; lower down. 



30 



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