AOIDIMETBY 21 



applied it would become turbid or thick, though on cooling it would become clear 

 again. 1 



A concentrated solution of lime in sugar being thus obtained, it should now be 

 diluted to such a degree that 1,000 water-grains' measure of it may be capable of satu- 

 rating exactly one equivalent of any acid, which is done as follows: Take 100 

 grains of hydrochloric acid of specific gravity 1-1812, that weight of acid contains 

 exactly one equivalent =36 '5 of pure hydrochloric acid gas ; on the other hand, fill 

 the acidimeter up to (zero) with the solution of caustic lime in sugar prepared as 

 abovesaid, and pour the contents into the acid until exact neutralisation is obtained, 

 which is known by testing with litmus-paper in the usual manner already described. 

 If the whole of the 100 divisions of the acidimeter had been required exactly to 

 neutralise the 100 grains' weight of hydrochloric acid of the specific gravity mentioned; 

 it would have been a proof that it was of the right strength ; but suppose, on the 

 contrary, that only 50 divisions of the lime solution in the acidimeter have been suffi- 

 cient for the purpose, it is evident that it is half too strong, or, in other words, one 

 equivalent of lime ( = 28) is contained in those 50 divisions instead of in 100. Pour, 

 therefore, at onco, 50 divisions or measures of that lime-liquor into a glass cylinder 

 accurately divided into 100 divisions, and fill up the remaining 50 divisions with water ; 

 stir the whole well, and 100 divisions of the lime-liquor will, of course, now contain 

 as much lime as was contained before in the 50 ; or, in other words, 100 acidimetrical 

 divisions will now contain 1 equivalent of lime, and therefore will be capable of 

 exactly neutralising 1 equivalent of any acid. 



When, however, saccharate of lime is used for the determination of sulphuric acid, 

 it is necessary to dilute it considerably, for otherwise a precipitate of sulphate of lime 

 would be produced. This reagent, moreover, is evidently applicable only to the deter- 

 mination of such acids the lime salts of which are soluble in water. 



Instead of a solution of caustic lime in sugar, a clean dry piece of white Carrara 

 marble may bo used. Suppose, for example, that the acid to be assayed is acetic acid, 

 the instructions given by Brando are as follows : A clean dry piece of marble is 

 selected and accurately weighed ; it is then suspended by a silk thread in a known 

 quantity of the vinegar or acetic acid to be examined, and which is cautiously stirred 

 with a glass rod, so as to mix its parts, but without detaching any splinters from the 

 weighed marble, till the whole of the acid is saturated, and no further action on the 

 marble is observed. The. marble is then taken out, washed with distilled water, and 

 weighed ; the loss in weight which it has sustained may be considered as equal to 

 the quantity of acetic acid present, since the atomic weight of carbonate of lime ( = 50) 

 is very nearly the same as that of acetic acid ( = 51). Such a process, however, is 

 obviously less exact than those already described. 



But, whichever base is employed to prepare the test-liquor, it is clear that the 

 acid tested with it must be so far pure as not to contain any other free acid than that 

 for which it is tested, for in that case the results arrived at would be perfectly falla- 

 cious. Unless, therefore, the operator has reason to know that the acid, the strength 

 of which has to be examined by that process, is genuine of its kind, he must make a 

 qualitative analysis to satisfy himself that it is so ; for in the contrary case the acid 

 would not be in a fit state to be submitted to an acidimetrical a'ssay. 



The strength of acids may also be ascertained by determining either the volumes or 

 the weight of carbonic acid gas disengaged from pure bicarbonate of soda by a given 

 weight of any acid. 



For measuring exactly the volumes of carbonic acid thus expelled, Dr. Ure's appa- 

 ratus, represented in fig. 7, may be used. As it is absolutely requisite, for the 

 success of the experiment, that the whole of the acid taken for examination should be 

 completely saturated, the operator must accordingly take care to use a little more 

 bicarbonate than is necessary for the purpose. 



Now the equivalent number of bicarbonate of soda is 75, and the carbonic acid 

 contained therein =44; that of oil of vitriol is 49 ; wherefore by mixing together 75 

 grains of pure bicarbonate of soda with 49 grains of pure oil of vitriol, 44 grains of 

 carbonic acid gas will be expelled, equal in bulk or volume to 2,381 acidimetrical 

 divisions (23,810 water-grains' measure). These proportions, however, would be 

 inconvenient, the more especially as the acidimeter in question should contain exactly 

 10,000 water-grains' measure, marked in series of 10 divisions from (zero) at the top 

 down to 100, such an arrangement at onco enabling the operator to read off the amount 

 of real acid per cent. ; and accordingly a weight, or proportion of acid capable of dis- 

 engaging exactly 10,000 water-grains' measure of carbonic acid from a quantity of 



1 The directions given by M. Violetto for the preparation of Saccharate of Lime are as follow : 

 Digest in the cold 50 grammes of slaked caustic lime in 1 litre of water containing 100 grammes of 

 sugar. 



