142 Biographical Account of Dr. Wollaston, hy Dk. Thomas TiiOJtsox. 



5. The next paper of Dr. Wollaston which I shall notice, was inserted 

 in the Philosophical Transactions for 1814, and was entitled a Synopti- 

 cal Table of Chemical Equivalents. It had been observed by Richter, 

 that when solutions of two neutral salts which decompose each other are 

 mixed, the new salts formed are always equally neutral. Thus, if 9 parts 

 of sulphate of soda be mixed with 16'25 parts of nitrate of barytes, the 

 two neutral salts will be converted into 1 0-5 parts of nitrate of soda and 

 14-6 of sulphate of barytes, the sulphate of barytes will precipitate, and 

 the nitrate of soda will remain in solution, Riehter found this law to 

 hold in all the cases tried, and thence inferred that the ratios of satura-, 

 tion of acids and bases, were always the same. Thus, 4 by weight of 

 soda will just saturate 5 of sulphuric acid, 6'75 of nitric acid, 7"25 of 

 arsenic acid, 4-5 phosphoric acid. Dr. Wollaston explained this remark- 

 able property by means of the atomic theory of Dalton. Acids and 

 bases unite atom to atom, or one atom of the one with 1 or 2 or more 

 atoms of the other. He showed, by a most laborious investigation, that 

 the same law holds in all chemical combinations. Metals combined with 

 one two or more atoms of oxygen to form oxides, with two or more atoms 

 of sulphur to form sulphurets. Every body has a peculiar atomic weight. 

 This he determined in a very considerable number ; drew up a table of 

 atomic weights referred to oxygen as imity, and transferring them to a 

 sliding scale, enabled the practical chemist to see at once the weight of 

 any body necessary to saturate an atom of any other. These scales were 

 exposed to sale, and at one time were very common in laboratories. But 

 the vast number of names upon the scale, made it difficult to discover the 

 name wanted, and on that account they have gradually gone out of use. 



6. In the year 1813 a paper by Dr. Wollaston was published in the 

 Philosophical Transactions, giving an account of a very ingenious mode 

 of showing the cold induced in water by evaporation. To the apparatus 

 used he gave the name of cryophorus. It consisted of a glass tube 

 about \ of an inch in diameter, terminating at each extremity in a glass 

 ball about one inch in diameter. This tube was bent at a right angle 

 about half an inch from each ball. One of these balls should contain a 

 little water. This water is boiled till all the air is driven out of the balls 

 and tube. The tube is now hermetically sealed and allowed to cool. 

 The water is then collected in one ball, while the other at the distance 

 of the tube, is plunged into a freezing mixture. By this contrivance the 

 vapour as it rises from the water is condensed, and thus the evaporation 

 from the water is continued unabated. The cold generated by this 

 evaporation is so great, that in a few minutes the water in the remote 

 bulb is converted into ice. 



7. There is still a paper of Dr. WoUaston's to be noticed. I mean his 

 examination of urinary calculi. It was published in the Philosophical 

 Transactions for 1797, and was indeed the first of his publications. One 

 species of urinary calculi had been examined by Scheele, who showed 

 that it was composed of a peculiar acid substance which exists in urine, 



