OF ARTS AND SCIENCES. 261 



phuric acid and careful expulsion of the excess of this last by heat. 

 I have found it more convenient to mix the oxalate intimately with an 

 excess of ammonic sulphate and heat carefully in a muffle, as in the 

 last case. The resulting sulphates are perfectly soluble without pack- 

 ing together if sifted upon the surface of cold water. They are also 

 perfectly neutral. The oxalates may also be converted into chlorides 

 by mixing them intimately with ammonic chloride and igniting the 

 mixture in a muffle very gently. 



Determinations of mean atomic mass are now always employed in the 

 study of the mixtures of oxides which present themselves in the attempt 

 to effect separations. Very accurate results are obtained by the usual 

 method of converting a weighed quantity of oxides into the equivalent 

 weight of sulphates by treatment with sulphuric acid and subsequent 

 careful ignition. Probably this could be done more conveniently, and 

 in less time, by igniting the oxides in porcelain crucibles in a muffle, 

 after mixing carefully with ammonic sulphate, but upon this point 

 I have made no quantitative experiments. 



In all my work I have employed the analysis of the oxalates as 

 convenient and accurate. It is, however, necessary to insist upon 

 several points of detail. In the first place I remark that the prepara- 

 tion of perfectly homogeneous mixtures of the oxalates requires much 

 care. It is best to precipitate by a hot dilute solution of oxalic acid 

 added slowly in small but distinct excess to a hot dilute solution of 

 the mixed chlorides or nitrates. The precipitated oxalates are then to 

 be thoroughly washed by decantation with hot distilled water. This 

 requires in general a large quantity of water, and must be continued 

 until the washings contain no trace of oxalic acid and give no cloudiness 

 with ammonia. Auer von Welsbach's process, which consists in adding 

 a very dilute solution of the nitrates (or chlorides) to a hot dilute 

 solution of oxalic acid, gives the oxalates in a state of very fine sub- 

 division and perfectly free from hard masses. The mixed washings 

 on saturation with ammonia sometimes give a precipitate of oxalates, 

 though in small quantity. These oxalates may be washed and mixed 

 with the main portion. The mass is to be dried upon a water-bath, 

 and then thoroughly mixed in a dry mortar. Only in this manner 

 is it possible to obtain a mass of oxalates sufficiently homogeneous 

 to yield corresponding results when different portions are analyzed. 

 The determination of tlie mean atomic mass in the oxalates prepared 

 as above involves only the determination of the percentages of oxide 

 R0O3 and of C.2O3, the water present being of course without influence. 

 Here I may remark that, as has doubtless been observed by other 



