88 ALKALIMETRY 



carbonates, and for a description of "which the reader is referred to the article on 

 ACIDIMBTRY. The ingenious little apparatus of Drs. Fresenius and Will for the same 

 purpose, and to -which we have already alluded in the same article, gives accurate 

 results ; but it should bo observed that -when the potash or soda of commerce contains 

 any caustic alkali, or bicarbonate, or earthy carbonates, or sulphuret of alkali -which, 

 as -we have seen, is frequently, and, indeed, almost invariably, the case, the process is 

 no longer applicable -without first submitting the sample to several operations which 

 render this process troublesome and unsuited to unpractised hands. Thus, if caustic 

 potash is present, the sample must be first mixed and triturated with its own weight of 

 pure quartzose sand and about one-third of its weight of carbonate of ammonia. The 

 mass is then moistened with aqueous ammonia, and then put into a small iron capsule 

 and evaporated to dryness, so as to expel completely 

 the ammonia and carbonate of ammonia. The mass is 

 then treated by water, filtered, washed, and concen- 

 trated to a proper bulk by evaporation, transferred to 

 the apparatus, and treated as will be seen presently. 

 If the sample contains caustic soda, instead of one- 

 third, at least half of its weight of carbonate of 

 ammonia should be employed. But for the estimation 

 of pure carbonates, Drs. Fresensius and Will's method 

 is both accurate and easy. The apparatus consists of 

 two flasks, A and B ; the first should have a capacity 

 of from two to two ounces and a half ; the second, 

 or flask B, should be of a somewhat smaller size, 

 and hold about one and a half or two ounces. Both 

 should be provided with perfectly sound corks, each 

 perforated with two holes, through which the tubes 

 a, c, d are passing. The lower extremity of the tube a 

 must be adjusted so as to reach nearly to the bottom 

 of the flask A, and its upper extremity is closed by means of a small pellet of wax, b ; 

 c is a tube bent twice at right angles, ono end of which merely protrudes through 

 the cork into the flask A, but the other end reaches nearly to the bottom of the flask B. 

 The tube d of the flask B merely protrudes through the cork into the flask. 



94. The apparatus beingso constructed, a certain quantity 100 grains, for example 

 of the potash or soda ash under examination (and which may have been previously 

 dried) is weighed and introduced into the flask A, and water is next poured into this 

 flask to about one-third of its capacity. Into the other flask, or flask B, concentrated 

 ordinary sulphuric acid is poured, and the corks are firmly put in the flasks, which 

 thus become connected, so as to form a twin-apparatus, which is then carried to a 

 delicate balance, and accurately weighed. This done, the operator removes the appa- 

 ratus from the balance, and applying his lips to the extremity of the tube d, sucks 

 out a few air-bubbles, which, as the other tube, a, is closed by the wax pellet, rarefies 

 the air in the flask A, and consequently causes the sulphuric acid of flask B to ascend 

 a certain height (after the suction) into the tube c ; and if, after a short time, the 

 column of sulphuric acid maintains its height in the tube c, it is a proof that the 

 apparatus is air-tight, and therefore as it should be. This being ascertained, suction 

 is again applied to the extremity of the tube d, so that a portion of the sulphuric acid 

 of the flask B ascends into the tube c, and presently falls into the flask A, the quantity 

 which thus passes over being, of course, proportionate to the vacuum produced by the 

 suction. As soon as the acid thus falls in the water containing the alkaline carbonate 

 in the flask A, an effervescence is immediately produced, and as the carbonic acid dis- 

 engaged must, in order to escape, pass, by the tube c, through the concentrated sul- 

 phuric acid of the flask B, it is thereby completely dried before it can finally make its 

 exit through the tube d. The effervescence having subsided, suction is again applied 

 to the tube d, in order to cause a fresh quantity of sulphuric acid to flow over into 

 the flask A, as before ; and so on, till the last portion of sulphuric acid sucked over 

 produces no effervescence, which indicates, of course, that all the carbonate is decom- 

 posed, and that, consequently, the operation is at an end, A powerful suction is now 

 applied to the tube d, in order to cause a tolerably large quantity of sulphuric acid, 

 but not all, to flow into the flask A, which thus becomes very hot, from the combina- 

 tion of the concentrated acid with the water, so that the carbonic acid is thereby 

 thoroughly expelled from the solution. The little wax pellet which served as a 

 stopper is now removed from the tube d, and suction applied for some time, in order 

 to sweep the flasks with atmospheric air, and thus displace all the carbonic acid in 

 the apparatus, which is allowed to become quite cold, and weighed again, together 

 with the wax pellet, the difference between the first and the second weighings that is 

 to say, the loss indicating the quantity of carbonic acid which was contained in the 



