24 



ACIDIMETRY 



11 



For sulphuric acid, for example, the proportion would be as follows : 

 2 C0 SO* 



44 : 40 :: 10 : x 



x = 9-09 (or moro correctly, 9'1). 

 Applying this rule, the weights to bo taken are as follows, in reference to 



Dry sulphuric acid 9'1 



nitric acid . . . . . . 12-27 



hydrochloric acid 8 '29 



acetic (dry) 11'59 



Crystallised tartaric acid .... 34-09 

 citric acid 43'64 



Each of these quantities of real acid, with 25 or 26 grains of bicarbonate of soda, 

 will give off 10 grains of carbonic acid gas ; and hence, by adding a cypher, that is, 

 multiplying by ten, whatever weight the apparatus loses denotes the per-centago of 

 acid in the sample under trial, without the necessity of any arithmetical reduction. 

 Let us suppose, for example, that the apparatus, being charged with 9-1 grains of a 

 sample of sulphuric acid, is found, after the experiment, to have lost 7'5 grains ; this 

 multiplied by 10 = 75-0 ; therefore the sample contained 75 per cent, of dry sulphuric 

 acid. If the apparatus had lost 2-44 grains thus, it would have indicated 24-4 per cent. 

 of dry or anhydrous acid. Persons accustomed to the French metrical system may use 

 decigrammes instead of grains, and they will arrive at the same 

 per-centage results. 



Another apparatus for ascertaining the weight of carbonic 

 expelled for the purposes of either acidimetry or alkalimetry, 

 and which the operator himself may readily construct, is repre- 

 sented in^. 11. 



A is a small matrass, with a somewhat wide mouth, capable, 

 however, of being hermetically closed by a cork perforated with 

 two holes, through one of which a bulbed tube, B, passes filled 

 with fragments of chloride of calcium ; through the other hole a 

 tube, c, is introduced, sufficiently long to reach the bottom of the 

 matrass A. 



A certain quantity (say 25 grains) of bicarbonate of soda, 

 greater than is required for saturation, is then introduced into 

 the matrass A, and likewise enough water to cover it. A small 

 glass test-tube is next charged with the proper quantity of the 

 acid to be examined, namely, 9'1 if for sulphuric acid, 12-27 if 

 for nitric acid, &c. &c., as before mentioned, and it is carefully 

 introduced into the matrass A, taking care that the acid does 

 not come in contact with the bicarbonate of soda, which is 

 easily avoided by lowering the tube containing the acid into the 

 matrass with a thread, or by carefully sliding it down, and 

 keeping it nearly in an upright position, leaning against the 

 sides of the matrass, as shown by the letter b. The matrass 

 is then to be closed with the cork provided with its tubes, as 

 above directed, and the whole is accurately weighed. This 

 done, the apparatus is gently jerked, or tilted, on one side, so 

 as to cause a portion of the acid in the tube b to flow among the 

 bicarbonate of soda on which it is resting. A disengagement of 

 carbonic acid gas immediately takes place from the decomposition of the carbonate 

 of soda by the acid. When the violent effervescence has subsided, a fresh quantity 

 of acid is again jerked, or spilled, out of the tube, until the whole of the acid is 

 emptied, the tube occupying now a horizontal position, as represented by letter a. 

 The water, which is mechanically carried off by the carbonic acid, is arrested by the 

 chloride of calcium of the bulbed tube B. When all disengagement of carbonic acid 

 gas has ceased, even after shaking the apparatus, the residuary gas is sucked up 

 through the bulbed tube B, while the atmospheric air enters at the orifice, d, of the 

 bent tube, c, to replace it. If the apparatus has become warm during the reaction, 

 it should be allowed to cool completely, and it is then weighed again accurately. 

 The difference between the first and second weighing, the loss, represents, of course, 

 the weight of the carbonic acid gas expelled, and consequently the per-centage of 

 real acid contained in the sample. 



Instead of the preceding arrangement, the apparatus contrived by Drs. Frosonius 

 and Will may be used. The annexed figure at once renders the construction of 

 that apparatus intelligible, and as a full description of it is given in the article on 

 AT.KATJMKTBY, the reader is accordingly referred thereto. When that contrivance is 



