22 



ACIDIMETRY 



bicarbonate more than sufficient to supersaturate it is used. That weight or portion 

 varies, of course, with each kind of acid, thus : 



Therefore by taking, of any sample of acid to be examined, the exact number of grains 

 corresponding to each of the above-mentioned acids, we shall obtain a volume of car- 

 bonic acid gas proportioned to the strength and purity of the 

 sample of each of them respectively. The modus operandi is 

 as follows : Charge the glass cylinder A with water, and pour 

 upon the surface of the latter a layer of olive oil, about 1 inch 

 in thickness, so that the level corresponds exactly to the (zero) 

 of the graduated scale etched on the glass cylinder. Through 

 the cork in the mouth of the cylinder, push the taper tail of the 

 flask c, air-tight ; introduce into this flask c about 50 grains of 

 bicarbonate of soda, in powder, and pour upon them a little more 

 water than is sufficient to cover the powder ; and if, for example, 

 the object is to determine the amount of pure oil of vitriol con- 

 tained in a given sample of that acid, weigh now accurately 

 20*58 grains of that sample, dilute it with water, and suck 

 it up into the taper dropping glass tube, D ; shut the stopcock, in- 

 troduce the dropping-tube, pushing it air-tight through the 

 perforated cork until its extremity plunges into the mixture 

 of bicarbonate of soda and water in the flask, c. On opening 

 now slightly the stopcock of the dropping-tube, the acid con- 

 tained therein coming in contact with the bicarbonate will cause 

 the evolution of a volume of carbonic acid proportioned to its 

 strength. Supposing the same sample of sulphuric acid which 

 was found by the acidimetrical process first described to contain 

 29-89 of oil of vitriol, or 24-4 of anhydrous sulphuric acid, per 

 cent., to be now examined by the present method, it will be 

 found that the 20'58 grains of that acid taken for the experi- 

 ment have disengaged a volume of carbonic acid gas corre- 

 sponding nearly to the number 30 of the graduated scale of the 

 glass cylinder, thereby indicating nearly 30 per cent, of pure 

 oil of vitriol in the sample under consideration. 



In the same manner the sample of hydrochloric acid, which 

 by the former process was found to contain 32-85 per cent, of 

 pure hydrochloric acid, would now disengage a volume of car- 

 bonic acid gas which would depress the level of the water in the 

 glass cylinder nearly to the point marked 33, and therefore 

 the operator would at once know that the quantity of pure hydrochloric acid gas 

 contained in the sample was a little less than 33 per cent., a degree of accuracy quite 

 sufficient for all commercial purposes, and which might besides be rendered still 

 more accurate by lengthening the glass cylinder and diminishing its bore, so that 

 the divisions may bo sufficiently distant as to admit of being subdivided into frac- 

 tions. 



The principal objection to this form of acidimeter, however, is its expense, and 

 also the difficulty or trouble of introducing into it the whole of the accurately weighed 

 quantity of acid, a circumstance which renders it less applicable to acidimetry than to 

 alkalimetry. By suppressing, however, the top flask, c, and using instead of it a 

 common Florence flask, connected with the cylinder, the cost is considerably reduced, 

 and the operator is at once enabled to secure the complete reaction of the whole 

 of the accurately weighed acid upon the bicarbonate of soda. The arrangement 

 has, besides, several other advantages, which the simple inspection of fig. 8 

 renders apparent. It consists of a 10,000 water-grains'-measuro glass cylinder, A, 

 graduated in the same manner, and provided with a discharge -tube, B, as before; 

 but the mouth of the cylinder need not be larger than that of an ordinary wine- 

 bottle, which allows of its being corked air-tight with greater ease and certainty. 

 This cork is perforated, and provided with a tube passing air-tight through it, and 

 connected by a length of vulcanised india-rubber, c with the disengagement tube of 

 an ordinary Florence flask, into which the bicarbonate of soda and a certain quantity 



