410 



CHEMISTRY. 



[OEOAXIC AXAIYKIS. 



to in a quantitative analysis conducted on the preceding 







If the article be a olid it must be most carefully 

 weighed, and atrtffw of hygromotric moisture should 

 be carefully ensure.! . If, however, a liquid be examined, 

 it should be inclosed in a glass tulx-. having a lino extre- 

 mity. Aftwr the tube has been w.-iiihed, tl.o liouid is 

 to be introduced by expelling the air by heat, and hold- 

 ii capillary owning beneath the surface of tlie 

 - .11 Uius be forced in by the pressure 

 o air. Tliu tube U then to be let down to the 

 okMed end, marked 6, in Fig. 77 ; and the remainder 

 (4 the oooibastifii tul is to be filled as before, with 

 oxide of copper. The process is to be conducted as 

 a. with Uie ex-pti..n, that a gentle heat is to be 

 applied to the end of the combustion tube holding the 

 liquid. This will expel a portion of the liquid, which, 

 pusiug as vapour to the heated portion of the oxide of 

 copper" will be decomposed. Of course, this operation 

 requires great care in manipulation ; and but a little at 

 a time of the liquid should be expelled, lest any portion 

 might escape combustion. 



The connections must all be as complete as possible, 

 so as to be quite air-tight. The only open part will be 

 the end of the potass apparatus. The latter should have 

 ree lower bulbs quite full, and the two upper, half 

 ailed. At first a little air will pass off, which, of course, 

 U owing to the expansion by heat of that contained in 

 the combustion tube. The chloride of calcium tube 

 must be accurately weighed when filled, each end being 

 fitted with corks, which arc to be weighed with it. 

 These, of course, are to be removed on using the tube, 

 but must be weighed again with it after the analysis is 

 concluded, as their absence would of course introduce a 

 source of error in the estimation of the increased weight 

 due to the absorption of water, resulting from the 

 combustion. 



The same remarks hold good with the potass appa- 

 ratus ; for the amount of carbonic acid produced is 

 known by the increase of weight, resulting from its 

 absorption by the liquid. It must therefore be accu- 

 rately weighed before and after the analysis, and the 

 increase of weight indicates the amount of carbonic 

 acid absorbed. At the moment of the analysis being 

 concluded, which will be noticed when the liquid potass 

 is not driven to and fro in the bulbs, the capillary end 

 of the combustion tube is to be broken, and by the 

 mouth or, still better, the end of a syringe or air-pump 

 attached by means of an india-rubber connection air is 

 to bo drawn through the whole apparatus ; and thus any 

 water or carbonic acid unabsorbed is drawn through the 

 calcium and potass tubes. It is true that a source of 

 r may arise from the admission of air ; but if this 

 :.-it carried to any excess, the error will be but 

 trilling. 



\\ lu-n nitrogen is present in any substance to be ana- 

 lysed, a separate analysis must be effected to determine 

 it> presence. In place of filling the potass apparatus 

 with that alkali, a solution of the chloride of plat ina is 

 to be employed. The substance under examination is 

 mixed with a portion of soda ash and lime, and heated 

 as before. By this means the nitrogen produces am- 

 monia, which, combining with the platina salt, forms 

 the double chloride of ammonium and platina, in which 

 form the nitrogen is estimated. The nature of the 

 double salt has already been referred to under the head 

 of Platina.* 



The delicate nature of organic analysis requires long 

 experience and great tact for its successful perform- 

 ance ; and we should far exceed the limits imposed 

 on us, were we to enter into every detail. Our object 

 has been to point out general outlines ; and we must 

 refer our readers to works on the subject, in which full 

 particulars are entered into, and every minutia* of the 

 prix*!Mcn which have been recommend are given in their 

 pnn i ..; ..-r. 



We may, however, just add, by wav of illustration, 

 the result* of an analysis in which we shall suppose that 

 * <, p. HI 



the amount of carbon, hydrogen, and oxygen has been 



law!. 



.-, a combustible substance has been 

 turned with oxide of copper, after the plans already 

 recommended ; and on weighing the chloride of calcium 

 .nid contents, we find that its increase is 2'25 grains ; 

 and the increase in weight of the potass apparatus and 

 contents, is 6-5 grains ; how much hydrogen, carbon, and 

 oxygen were present in the substance, supposing that it 

 liad weighed 3'75 gran 



1. We have 2 '25 grains of water produced therefore. 

 As the equiv. of water = 9 is to hydrogen 1, so is 



2-26 to -25. 



Or, As 9 : 1 : : 2 25 : -f- - '25 



J 



Hence we have of hydrogen '25 grains. 



And necessarily the rest is oxygen = 2'00 



2-25 



2. Now, we find that the contents of the potass 

 apparatus sustained an increase of 6 "5 grains. We 

 then-fore say 



As the equiv. of CO 8 = 22 is to C = 6, so is 5 5 to 15. 



Or, 



As 22 : C : : 55 

 6 



22)33-0(1-5 

 22 



110 



110 



In other words, the substance analysed contained 

 Of hydrogen '25 grams. 

 oxygen 200 

 ,, carbon 1'50 ,, 



Its original weight 3' 75 



If we wish to find the equivalents of each element 

 present, we shall easily obtain them by multiplying each 

 of the quantities in the above example by 4 ; thus 

 H = -25 X 4 = 1 = one equivalent. 

 O = 2-00 X 4 = 8 = 



C = 1-50 x 4 = 6 = 



Hence the supposititious substance is com posed of one 

 equivalent each, of hydrogen, oxygen, and carbon. We 

 must here mention that we have invented a substance 

 expressly for our purpose, so that it might contain only 

 one equivalent of each element. This has been done 

 only for the sake of simplicity ; and our readers can 

 easily extend our example to facts, by multiplying the 

 proportion, as given above, by the formulae for any 

 chosen body, maintaining of course the relative pro- 

 portions which exist therein. 



Thus, if 3-75 grains of ether had been analysed, its 

 foruiuia being C 4 + H s + O, we should have had 

 Of hydrogen = '507 grains. 

 oxygen = '811 

 carbon = 2 -432 



3700 ,, 



Now, as the weight employed is nearly one-tenth of 

 that of an equivalent of ether, which is 37, we shall 

 nearly obtain the equivalent of each of the substances, 

 by multiplying each of the above weights by ten. This 



result would be more exact if we used the factor tj "^. ; 



o 75 

 thus, the equivalent of the 



si i x :- _ ft 



2-432 X 37 

 376 



Carbon * - I 



Or, ether - 4 + H, -f - 37 



