OP ARTS AND SCIENCES. 9 



appear. In the first place, we are persuaded that in the determination 

 of atomic weights it is just such constant errors as we have encoun- 

 tered that are almost solely to be feared, and that the mechanical per- 

 fection of our analytical methods is far in advance of our chemical 

 knowledge of the materials and processes we employ. In the second 

 place, we feel assured that no agreement, however close, of results 

 obtained by the repetition of the same process, under the same condi 

 tions, gives any certain guarantee of the correctness of the atomic 

 ratio which is sought to be established ; and hence that in the present 

 state of science no certain conclusions can be reached in regard to the 

 validity either of Front's Law or of other numerical relations be- 

 tween the atomic weights of the chemical elements. 



We return now to our former position, — that in determining an atomic 

 weight it is of the first importance to show that the compound analyzed 

 is not only pure in the ordinary sense, but also that it contains the 

 elements to be compared in atomic proportions. And, after carefully 

 reviewing the whole subject in the light of our present knowledge, we 

 have been led to the conclusion that the most satisfactory evidence on 

 this point we can obtain is that furnished by a chemical reaction, in 

 regard to which it can be shown that the two elements under compari- 

 son are transferred without loss or elimination of material fr'om one 

 combination to another. Now, satisfiictory evidence of this kind may 

 be adduced in regard to the method of determining the atomic weight 

 of antimony employed by Schneider. The native sulphide of antimony 

 which he analyzed dissolves in hydrochloric acid with the evolution of 

 hydric sulphide, leaving no residue saving a minute amount of siliclous 

 gangue, which can be accurately estimated. If then sulphur is com- 

 bined in atomic proportions witii hydrogen in the gas evolved during 

 this reaction, it must also have been combined in atomic proportions 

 with antimony in the original compound ; for otherwise the metathesis 

 could not have taken place without an elimination of the excess of one 

 or the other of the constituents. To this familiar fact, we can add still 

 other evidence which makes the proof complete. In the first place, we 

 have repeatedly verified the statement of other chemists, that when — 

 as is always the case unless great care is taken — an excess of sulphur 

 is precipitated by the action of hydric sulphide on solutions containing 

 antiiuony, this excess, however small, is eliminated, and remains undis- 

 solved when the dried precipitate of Sb.^Sg is dissolved in pure hydro- 

 chloric acid. In the second place, during our investigation of the zinc 

 and antimony compounds above referred to, we prepared artificial crys- 

 tals of antimony glance containing several per cent of antimony in 



