ALKALIMETRY 57 



at 48-62 parts, make another line, and write potash ; still lower, at 54-43 parts, a third 

 line marked carb. soda, and at 65 parts a fourth, marked carb. potash. It will be ob- 

 served that portions are measured off beneath these marks in the inverse order of the 

 equivalent number of these substances, and consequently directly proportionate to the 

 quantities of any particular acid which will neutralise equal weights of the alkalis 

 and their carbonates. As these points are of great importance, it will be proper to 

 verify them by weighing into the tubes first 350, then 513-8, and lastly 779-9 grains 

 of water, which will correspond with the marks if they are correct, or the graduation 

 may be laid down from the surface of the four portions of fluid when weighed in, 

 without reference to where they fall upon the general scale. The tube is now com- 

 pleted, except that it should be observed whether the aperture can be perfectly and 

 securely covered by the thumb of the left hand, and if not, or if there be reason to 

 think it not ultimately secure, then it should be heated and contracted imtil suffi- 

 ciently small. 1 



29. The test acid for this alkalimeter should have a specific gravity of 1-1268 ; and 

 such an acid may be prepared by mixing one part, by weight, of sulphuric acid, 

 specific gravity T82, with four parts of water, and allowing the mixture to cooL In 

 the meantime, 100 grains of pure anhydrous carbonate of soda, obtained as indicated 

 before, should be dissolved in water, and the test sulphuric acid, of specific gravity 

 1-1268, prepared as above said, having become quite cold, is poured into the alkali- 

 meter up to the point marked carbonate of soda ; the remaining divisions are filled up 

 with water, and the whole should be well mixed by shaking. 



30. If the whole of the sulphuric acid, adjusted as was said, being poured carefully 

 into the solution of the 100 grains of the neutral carbonate of soda, neutralise them 

 exactly which is ascertained, as usual, by testing the solution with litmus-paper, 

 which should not be either reddened or rendered bluer by it it is of course a sign 

 that the test is as it should be that is to say, is of the proper strength ; in the con- 

 trary case it must be finally adjusted in the manner already indicated, and which 

 need not be repeated. See 20, 21. 



31. The best and most convenient process for the analyst, however, consists in 

 preparing a test acid of such a strength that it may serve not only for all alkalis, but 

 indeed for every base; that is to say, by adjusting the test acid so that 100 alkalime- 

 trical divisions of it (1,000 water-grains' measure) may exactly saturate or neutra- 

 lise one equivalent of every base. This method, which was first proposed by Dr. 

 Ure, is exceedingly convenient, and the possession of two reciprocal test liquids, 

 namely, the ammonia test liquor of a standard strength, of which we gave a descrip- 

 tion in the article on Acidimetry, and the standard test acid of which we are now 

 speaking, affords, as Dr. Ure observes, ready and rigid means of verification. For 

 microscopic analysis of alkaline and of acid matter, a graduated tube of a small bore, 

 mounted in a frame, with a valve apparatus at top, so as to let fall drops of any size 

 and at any interval, is desirable ; and such an instrument Dr. Ure employed for many 

 years ; but instead of a tube with a valve apparatus at top, the operator may use a 

 graduated tube of a small bore, terminated by a small length of vulcanised india-rubber 

 tube pinched in a clamp, which may be relaxed in such a way as to permit also the 

 escape of drops of any size at any interval of time, the little apparatus being under 

 perfect command. 



32. The test sulphuric acid, of such a strength that 100 alkalimetrical divisions of it 

 can saturate one equivalent of every base, should have a specific gravity of 1-032, 

 and is prepared as follows : 



Take 53 grains (one equivalent) of pure anhydrous neutral carbonate of soda, 

 obtained in the manner indicated before (see 18), and dissolve them in about one 

 fluid ounce of water. Prepare in the meantime the test sulphuric acid by mixing one 

 part, by measure, of concentrated sulphuric acid with about 11 or 12 parts of water, 

 and stir the whole well. The mixture having become quite cold, fill the alkalimeter 

 with the cold diluted acid up to the point marked 0, taking the under line of the 

 liquid as the true level, and whilst stirring briskly the aqueous solution of the 53 

 grains of carbonate of soda above alluded to, pour the acid carefully from the 

 alkalimeter into the vortex produced by stirring, until, by testing the liquor alternately 

 with reddened and with blue litmus-paper, or, more conveniently still, with grey 

 litmus-paper, the neutralising point is exactly hit. 



33. If the whole of the 100 divisions of the alkalimeter had been required to neu- 

 tralise exactly the 53 grains of pure anhydrous carbonate of soda, it would be a proof 

 that the acid is of the right strength ; but if this is not the case, it must bo adjusted 

 in the manner described before, that is to say : 



34. Let us suppose, for example, that only 50 measures in the alkalimeter have 

 been required to saturate or neutralise the 53 grains of carbonate of soda, then 60 

 measures should be poured at once into a glass cylinder accurately divided into 100 



