CHEMICAL ANALYSM. 



UII-.Mli-AL Kc.'IMVAI.KNTS. 



793 



liquid ounce*, an exeat of a lolutiuu of pure caustic potash IB added, 

 and the whole heated for a few minute* to boiling. The copper is 

 thereby completely precipitated a* black oxide ; thta u filtered from 

 the sulphate of potaah, and waahed a* before described. The filtrate 

 need not be kept The funnel u covered and dried as before. 



The crucible, whose weight is C, U now placed upon a sheet of 

 black gUied paper. The filter containing the sulphate of baryta i 

 unfolded, and a* much aa possible of the sulphate shaken into the 

 crucible. The sides of the paper are rubbed together to remove the 

 adhering sulphate. The filter u folded up again, and, being so rolled 

 together that all the edge* are inside, it is wrapped in a piece of 

 platinum wire, set on fire over the lamp, and held over the crucible. 

 It is then held above the lamp until all incandescence has ccasnd, and 

 perfect whitened U attained ; then being shaken into the crucible, 

 into which all particles which have been spilled are swept from the 

 paper by a feather, the whole U heated for half an hour to redness, 

 allowed to get cold as before, and weighed. Its weight is C + A + M ; 

 so that U U the weight of the sulphate of baryta (BaOSO,). From 

 .livalciit of barium being 68'6, that of oxygen 8, and that 

 of Milplmr 16, we know that the equivalent of sulphate of baryta 



Ba 

 

 S 

 O, 



= 68-6 



= 8- 



= 16- 



= 24- 



116-6 



That U, 116'6 parta by weight of sulphate of baryta contain 40 of S0 3 . 

 Hence the amount of sulphuric acid found in the sulphate of baryta, 

 that is, in the original sulphate of copper, is 



The oxide of copper is ignited and weighed in the same manner. 

 Let the crucible, filter ash, and oxide of copper, together weigh C + 

 A + N, then N is the weight of the oxide of copper. We have thus 

 found the absolute weights of the water, sulphuric acid, and oxide of 

 copper, contained in a given weight of sulphate of copper. If the 

 analysis has been performed with perfect accuracy, it is evident that 

 the sum of these three quantities should be identical with the weight 

 of the sulphate of copper taken. But in order to compare various 

 analyse* with one another in which different quantities of substance have 

 been employed, it is convenient, from the absolute weights so found 

 to deduce the amounts of the various constituents which would be 

 contained in 100 parts, by weight; in other words, to find their per 

 centage amount. 



If 8 grammes contain W grammes of water, 2 of sulphuric acid, and 



N of oxide of copper, then 100 grammes will contain W of water, 



S 



,100 



.100 



2 _ of sulphuric acid, and N _ of oxide of copper, and the sum of 



8 S 



these should, of course, be 100. In practice, however, this i very 

 rarely the case. Inaccuracies in weighing, imperfect insolubility of 

 precipitates, imperfect washing, inexact determination of equivalent*, 

 loss by manipulation, Ac., are sources of error which it is impossible 

 wholly to avoid. The exactness of an analysis, that is, the nearness to 

 100 to which the sum of it* per centage constituents amount*, depends 

 of course upon the nature and number of the substances to be deter- 

 mined ; an error of two- or three-tenths per cent, in each is generally 

 admissible. 



It U impossible to describe fully the methods and precautions used 

 in the quantitative determination of the various elements. 



Potassium U estimated as KC1, 1'tt'l,. 



Sodium as NaCM, or NaO SO,. 



Ammonium u NH.C1, PtCl^ or .from the amount of platinum which 

 this salt contains, 



Lime aa CaO CO,, derived from the gentle ignition of the insoluble 

 oxalate. 



Strontia aa SrOSO,, which U insoluble in alcohol. 



Baryta as BaO SO,. 



M.giv^u 2MgO I'O, derived from the ignition of the insoluble 

 2HgONH.OPO r 



Iran u F,O, 

 Aluminium u AI,O, 

 Chromium u Cr,O, 

 ItennneM u Mn'O* 



Nicki-1 a* K10 

 Cobalt u Co 



The acid* are estimated 



Hydrochloric 

 llyilrlodic 

 Ilydrobromle 

 Hronejiulo 



Aram leu Art. 



TlnuBnO, 

 Gold V 



Platinum j u mrtali. 

 Mercury ) 

 Ixwd u PbO fO, 

 Mirer si AgCl 

 Bismuth an Wo, 

 Cadmium u CdO 

 Copper u CuO. 



I addsas 1 



AC1 



N.c ', 



Carbonic acid by the loss in weight experienced on its expulsion. 



Sulphuric as BaOSO,. 



Hydn mulphiiric by conversion into sulphuric, as BaOSO,, or as AsS,. 



Bondo H !'< ' . 



Silicic as SiO,. 



Phosphoric as 2MgO PO,, derived from the ignition of the insoluble 

 2MgONH,OPO.. 



Oxalic from the amount of CaOCO., found on igniting the insoluble 

 CaOC.O,. 



Chloric from the amount of chloride formed on igniting its salts. 



Nitric from the quantity of Cu it dissolves in the presence of hydro- 

 chloric acid. 



Sometimes one of two substances which are nearly allied and which 

 occur together, is estimated by deficiency. Thus, if we have a weighed 

 quantity of the mixed chlorides of sodium and potassium, the chloride 

 of potassium contained in the mixture is determined by estimating the 

 amount of KC1, PtClj to which it gives rise, the amount of chloride of 

 sodium is the difference between the weight of the mixed chlorides 

 and that of the chloride of potassium. Or again, if we have a mixed 

 chloride and iodide of potassium, the two halogens are combined with 

 silver, and a weighed quantity of the mixed silver salts being taken, is 

 subjected to the action of a stream of dry chlorine. The chlorine 

 replaces the iodine, and the loss experienced thereby in weight is the 

 ditt'iTeiiee betwwn the iodine which has been driven out anil the 

 chlorine which has entered. The quantity of iodine, and hence that 

 of chlorine, may be thence easily calculated. 



( ' H EMICAL COMBINATION. [CHEMICAL Aprnnrnw.] 



CHEMICAL EQUIVALENTS. The term chemical equivalent is 

 frequently used as synonymous with the expressions atomic wciy/it ,-md 

 combining proportion ; strictly, however, it U by no means synonymous 

 with these terms ; since the equivalent of a body may be, and occa- 

 sionally is, different from its atomic weight or combining proportion. 

 An equivalent of a substance obviously means such a weight or volume 

 of that substance as is required to replace another body in a definite 

 chemical compound. Thus if we take the element hydrogen and com- 

 bine it with iodine, we find that 1 Ib. of hydrogen combines with 

 exactly 126-88 Iba. of iodine. Now if the hydriodic acid thus formed 

 be brought into contact with a sufficient quantity of bromine, the 

 iodine will be expelled and its place occupied by the bromine, of which 

 exactly 79'97 Ibs. will have taken the place of tide 126'88 Ibs. of iodine. 

 The bromine compound may in like manner be decomposed by 

 chlorine, and it is found that only 35'49 Ibs. of chlorine are required 

 to replace or expel the 79'97 Ibs. of bromine. Finally, oxygen may be 

 made to replace the chlorine when 8 Ibs. of oxygen ore found to be 

 capable of expelling the whole of the chlorine. It is therefore obvious 

 that 126-88 Ibs. of iodine, 79'97 Ibs. of bromine, 86'49 Ibs. of chlorine, 

 and 8 Ibs. of oxygen, are equivalent to each other in chemical com- 

 bination, but a reference to the table of atomic weights [ATOMIC 

 THEORY], shows that these numbers are also the atomic weights of the 

 respective elements. If, however, we now replace the oxygen contained 

 in the compound last mentioned, with nitrogen, phosphorus, arsenic, 

 or antimony, we find that the weights of these elements required to 

 replace the 8 Ibs. of oxygen are respectively 47, 107, 25, and 43, 

 numbers which do not coincide with the atomic weights or combining 

 proportions of these elements, but which ore exactly one-third of those 

 weights. In other words, in these cases the atomic weight of the 

 element is made equal to three times its equivalent number, and we 

 formulate the hut-mentioned compounds as follows : 



Ammonia 



I'ho]ihurottod hydrogen I'll 



Arncnurctu-d hydrogen Ali 



Antimonurcttcd hydrogen fbll 



MI, 

 I 



The reasons for departing from the general rule in these cases may 

 be thus stated, in the case of nitrogen, and many of them apply also 

 with equal force to the other elements in question : 



1. Because it is found that a given bulk of gaseous ammonia contains 

 three times as much hydrogen as the same bulk of hydrochloric acid 

 (HC1). 



2. Because it is found that a given bulk of nitrogen combines with 

 three times as much hydrogen as does the same bulk of chlorine ; .-ui.l 

 that the relative weights of equal bulks of nitrogen, chlorine, and 

 hydrogen are as 14 : 85-49 : 1. 



8. Because certain undoubted analogies are concealed if the com- 

 bluing pro|Mirtinn of nitrogen be taken a* 47, whilst they ore rendered 

 evident if the number 14 be adopted. 



4. Because in nearly every case the quantity of ammoni.i \\Iii, <li 

 is the agent or resultant of a reaction, contains three atoms of hydrogen 

 or some multiple of three atoms of hydrogen ; and consequently four 

 teen, or some multiple of fourteen parts of nitrogen. 



6. Because, in ammonia, the replacement of hydrogen by other 

 bodies takes place definitely in thin Is by three successive stages. 



6. Became the formula) of the compounds of nitrogen with oxygen, 

 would be abnormal and without all analogy if the atomic weight of 

 nitrogen were taken at 4-7 whereof! the number 14 gives formula} 

 on account of the regular gradations which they exhibit, cause 

 ipoimds of nitrogen and oxygen to be very generally * 

 as illustrations of the law of multiple proportions. 



