422 Proceedings of the British Association. 



required 8 tons 1^ cwt., being a saving of 5 tons 8 cwt., for each' 

 ton of iron produced. This subject was discussed at considerable 

 length. 



Dr Christison then gave an account of some observations in regard 

 to the action of various waters on lead, and of some practical re- 

 sults deducible from them, relative to the use of lead in the con- 

 struction of water-pipes and cisterns, and the manufacture of carbo- 

 nate of lead. 



A communication was then read from Sir David Brewster, on 

 the optical characters of minerals, which gave rise to considerable 

 discussion. 



Mr Graham gave an account of an investigation made by him 

 into the constitution of certain hydrated salts. He stated that he 

 had found,^ — That certain salts of sulphuric acid which crystallize 

 with 5, 6, or 7 atoms of water, contain 4, 6, or 6 of these as water 

 of crystallization, which are expelled at or below 212° under at- 

 mospheric pressure, and at 60° in vacuo : That one atom is left as 

 essential to the constitution of the salt : That this remaining atom 

 of water is expelled by a stronger heat, and is in general recovered 

 on exposure of the anhydrous salt to the air ; and that in every 

 instance of a sulphate so constituted, the essential atom of water 

 may be displaced by sulphate of potass, which, in the proportion of 

 one atom, occupies the place of the expelled water, constituting a 

 crystallizable sulphate, with a double base and six atoms of water of 

 crystallization. The salts possessing these properties are the sul- 

 phates of zinc, iron, nickel, manganese, copper, lime, magnesia, 

 cobalt. 



Some applications of these and other facts were made by the 

 author, to the doctrine of Isomerism ; which led to a long and in- 

 teresting discussion between Drs Dalton, Thomson, Turner, Clark, 

 and Professor Johnston. 



JVIr Kemp next gave an account of a paper on a new mode of 

 liquefying the gases, by which they may be obtained more easily, 

 and in much larger quantity. He detailed the properties of se- 

 veral of the gases in the liquid state, illustrating more particu- 

 larly the independent bleaching power of chlorine, and sulphuretted 

 hydrogen when in a state of liquid, the power of some of the 

 condensed gases as conductors of electricity, and the phenomena 

 resulting where the condensed gases are brought in contact with 

 one another, as well as with other substances. 



The Section then adjourned till the 13th at half-past ten aj^. 



