OP ARTS AND SCIENCES. 625 



Before the publication of these papers upon the vermiculites, 

 Professor Cooke had begun the study of antimony, and was able to 

 present to the Academy, in June, 1873, a preliminary notice of some 

 determinations of its atomic weight. So many ditficulties were en- 

 countered, however, that the extended paper upon the subject did not 

 make its appearance until four years later. In 1854 he had expressed 

 the opinion that the accidental errors affecting such determinations 

 could easily be eliminated, while the constant errors were the great 

 eri-ors involved. In 1877 he closes the account of his revision of the 

 atomic weight of antimony with the remark that the investigation 

 from the first had been a study of constant errors. It is not possible 

 to tell briefly the story of the persevering search for these constant 

 errors, — a search involving months of patient labor. I could but re- 

 peat the words with which Professor Cooke has himself described, 

 with painstaking fidelity, the steps which he took in surmounting the 

 successive difficulties. The hardest task, possibly, was to show the 

 constant error which vitiated the results obtained by Dumas twenty 

 years before, — results which had been welluigh universally accepted. 



The careful study of the compounds of antimony with the halogens, 

 which was a necessary preliminary to the determination of its atomic 

 weight, established many interesting facts, the most important of 

 which, possibly, was the existence of three different crystalline forms 

 of antimonious iodide belonging, respectively, to the monoclinic, ortho- 

 rhombic, and hexagonal systems. The results of the quantitative 

 study of antimonious bromide, confirming the value of the atomic 

 weight of antimony which he had previously established, were given in 

 a paper which appeared a year or two later, and the advantage which 

 could be gained by the simultaneous determination of three atomic 

 ratios was here discussed. The evidence was now complete, and the 

 new atomic weight of antimony was adopted by the whole chemical 

 world. A series of less important papers appeared during the pro- 

 gress of this work upon antimony, describing new methods devised for 

 the work, or discussing details of the processes involved. Among 

 them may be mentioned " A new method for manipulating hydric 

 sulphide," '•' The process of reverse filtering," " Argento antimonious 

 tartrate," and " The solubility of chloride of silver in water." 



Shortly after the completion of the work upon antimony. Professor 

 Cooke planned an investigation upon the relative values of the atomic 

 weights of oxygen and hydrogen. The necessary exploratory work 

 upon this research was delayed by failing sight and precarious health, 

 so that it was not until the autumn of 1886 that everything was ready 



