248 KEPOET— 1889. 



is, therefore, heated in chlorine, and is found to increase in weight to the 

 same extent as when it is dissolved in nitric acid, &c. ; a given weight of 

 silver precipitated by salt is also found to increase to the same extent as 

 when it is directly combined with chlorine. The composition of silver 

 chloride having thus been ascertained, the amount of chlorine in salt is 

 determined. The composition of salt being ascertained, purified dried 

 washing soda is converted into salt, and also the amount of chalk gas 

 which it contains is determined : from the data, the composition of sodiam 

 oxide may be calculated. In like manner the composition of lime may be 

 ascertained by converting chalk into chloride by igniting it in hydrogen 

 chloride, and then determining the chlorine in the chloride ; the same 

 method may be applied to the determination of the composition of the 

 oxides and chlorides of zinc, magnesium, and copper. 



Discussing these various results, and comparing the quantities of 

 oxygen and of chlorine which combine with any one of the metals examined, 

 it is seen that in every case about 35'4 parts of chlorine take the place of 

 eight parts of oxygen. Combination in reciprocal proportions is thus 

 illustrated, and by considering the composition of chalk and washing 

 soda it may be shown that this applies equally to compounds of two and 

 to compounds of three elements. As 35 '4 parts of chlorine are found in 

 every case to correspond to eight parts of oxygen, it is to be expected 

 that hydrogen chloride contains one part of hydrogen in combination with 

 35'4 parts of chlorine ; a solation containing a known weight of hydrogen 

 chloride is, therefore, prepared by passing the gas into a tared flask 

 containing water and the chlorine is then determined. 



It being thus clearly established what are equivalent weights of 

 elements, the conception of equivalents may be further developed by 

 exercises in acidimetry carried out by the pupils themselves. The pro- 

 portions in which washing soda and hydrogen chloride interact may be 

 determined by mixing solutions of known strength until neutralisation is 

 effected ; if the solution be evaporated and the chloride weighed, the 

 results may be used in calculating the composition of hydrogen chloride ; 

 they serve, in fact, as a check on the conclusions previously arrived at as 

 to the composition of washing soda and hydrogen chloride. Solutions 

 of sulphuric and nitric acid may be similarly neutralised, and, the amounts 

 of sulphate and nitrate formed having been ascertained, the equivalents 

 of the acids may be calculated on the assumption that the action is of the 

 same kind as takes place in the case of hydrogen chloride. Determinations 

 of the strengths of acids, &c., may then be made. In a similar manner 

 the volumetric estimation of silver may be taught and the percentage of 

 silver in coinage and other alloys determined. 



Such a series of quantitative exercises as the foregoing, when carried 

 out before and to a considerable extent hij the pupils, undoubtedly affords 

 mental discipline of the very highest order, and is effective of good in so 

 many ways that the value of such teaching cannot be over-estimated. 

 The failure to grasp quantitative relationships which examiners have so 

 frequently to deplore is without question largely, if not alone, due tO' 

 students' entire ignorance of the manner in which such relationships hav^e 

 been determined. Moreover, the appreciation by the general public of 

 the principles on which quantitative analysis is founded would cer- 

 tainly be directly productive of good in a multiplicity of cases. 



