The late Dr. Thomas Thomson. 261 



the tritoxide the third, and so on — the term peroxide being given to 

 that in which the metal is united to a maximum of oxygen. When it was 

 discovered that in a supersalt the proportion of acid to the base was 

 twice as great as in the neutral salt, Dr. WoUaston, to denote that rela- 

 tion, prefixed the Latin word bis to the acid of the supersalt. In the 

 same way he gave the name quadroxalate to a salt of potash in which the 

 proportion of acid to the base was four times as great as in the neutral 

 salt. When the base is doubled, Dr. Thomson denotes this by prefixing 

 to the name of the acid the Greek syllable dis ; and for salts having three 

 and four times the proportion of base, tris, tetrakis, &c. 



As an analyst. Dr. Thomson, by his earlier experiments, which are ex- 

 ceedingly numerous, contributed greatly to the advancement of the science, 

 when it needed such information. His analyses professed to be nothing 

 more than approximations to the truth, and they served their purpose 

 well. But after the atomic theory was established, and the question became, 

 to determine the weights of the equivalents of bodies, a degree of pre- 

 cision was required, which till then had been practised in but few cases, 

 and which indeed the means at their disposal seldom enabled chemists to 

 attain. After the part which, as we have seen. Dr. Thomson took in 

 promulgating the principles of Daltou and of Prout, he undertook a great 

 amount of labour for the purpose of establishing, bj' experiment, the 

 weights of the elements. His experiments on the specific gravities of the 

 gases confirmed most exactly the numbers of Prout. They were performed, 

 with the assistance of Mr. Alexander Hai'vey, with great care — minute 

 particulars are given of the methods employed ; and the sei'ies attracted 

 none of the severe animadversions that have been bestowed upon the 

 analyses of the salts. 



The results of five years' labour upon the salts were published in 1825 

 in the two volumes forming the " Attempt to establish the First Princi- 

 ples of Chemistry by Experiment." The principal method employed 

 was that by double decomposition, used with great advantage by Wenzel. 

 A quantity of muriate of barytcs, for example, was weighed and dissolved 

 in distilled water. A quantity of sulj)hate of potash, nearly an equivalent 

 of the first, was also weighed and dissolved. The two solutions were 

 mixed together and filtered, and the liquid was tested for barytes and for 

 sulphuric acid. If barytes was indicated, the mixture was made anew, 

 with an additional portion of sulphate, and vice versa — the process being 

 repeated until a point was found at which no precipitate occurred on the 

 addition of either salt. The atomic weight of one of the salts being 

 known, the experiment decided that of the other. No attempt was made 

 to collect the two new salts formed in the process. The proportions of the 

 constituents of a great number of salts were thus determined ; and hero 

 the confirmation given to the original numbers of Dr. Prout, was not only 

 complete, but if taken literally, wa.s altogether marvellous. 



It is to be regretted that the examination of this work should not have 

 been conducted in a better sjjirit. Tiiere were, no doubt, causes of irrita- 



