408 Proceedings of the British Association. 



Mr Van der Toorn next gave a determination of the amount 

 of water in crystallized sulphate of zinc. The total amounts to 7 

 atoms, of which 6 are given oflF at 110° C, the other atom remaining 

 as a necessary constituent of the salt. From this result he con- 

 cluded that sulphates, which at a red heat give off sulphuric acid, 

 contain an atom of water as an essential constituent. On this subject 

 some discussion arose, and Dr Clarke stated as a general law, that 

 when salts effloresce, they always form compounds containing a de- 

 finite number of atoms of water, which compounds may be obtained 

 regularly crystallized by submitting solutions to evaporation at dif- 

 ferent temperatures. 



Some considerations were then submitted by Mi* Johnston on 

 chemical notation, which gave rise to a discussion in which many 

 members of the section took part. The result was, that the subject 

 of notation was referred to the Committee of the Section with 

 the view of introducing into this country a uniform system of no- 

 tation. 



A model of a spirit of wine lamp of considerable power, by Mr 

 Trevelyan, was exhibited. After which a paper was read by Mr 

 Henry Hough Watson, on the amount of carbonic acid in the 

 atmosphere of the town of Bolton, and the country around. 



His results were in 10,000 parts, 



Max. 

 In the country, [12 observations] = 4.74 

 In the town, [19 observations] = 8 62 



He could not discover any connexion between the variations of its 

 quantity, and season, and weather, as suggested by De Saussure. 

 The method adopted by Mr Watson to determine the point, did 

 not appear, however, entirely free from objection. In the course 

 of the discussion which arose, Dr Thomson stated as his opinion, 

 that the difference in the results obtained at different times, and by 

 different experimenters, arose from errors of experiment. 



An extract of a letter was then read from Professor Hare of 

 Philadelphia, suggesting the propriety of appointing agents in the 

 different ports to assist the members of the Association in com- 

 municating with foreigners. 



It was also stated by the Secretary, that an able report had been 

 received from Dr William Henry on the present state of our 

 knowledge regarding contagion. 



An analysis of the oxichloride of antimony or crystallised pow- 

 der of Algaroth by Mr Johnston, was then read, after which the 

 meeting adjourned to Friday the 12th, at 11 o'clock. 



