Mr. Couper on the Chemical Composition of Pottery. 171 



were paid,' leaving a balance of receipts over expenditure, now in the 

 Union Bank, of £453 8s. 10d., which, with £7 2s. lOd. of interest to the 

 20th of April, current, leaves an available balance of £460 lis. 8d., to 

 be laid aside for future exhibitions of a similar kind, in conformity with 

 article 5 of contract agreement betwixt the Town Council and the Philo- 

 sophical Society, of date 1st April, 1846, which runs thus — " If it should 

 happen that, in place of a loss, there should be an overplus of money 

 received, said overplus to be laid aside as a fund for future exhibitions of 

 a similar nature." Mr. Liddell moved, agreeably to a recommendation 

 contained in the Acting Committee's report to the General Committee on 

 the exhibition, and adopted by the latter on the 20th April, " that this 

 money, in the meantime, be lodged with the Corporation of the City, at 

 the current rate of interest, in name of the Lord Provost and Senior 

 Bailie of Glasgow, ex officio, and of the President and Vice-President of 

 the Philosophical Society, also ex officio, as trustees for the application of 

 this sum; and that the Treasurer of the Philosophical Society for the 

 time being, bo the custodiers of the bill or other voucher for the debt; 

 and that he bo requested to seo that the interest be added to the principal 

 sum twice every year, at the usual terms of Martinmas and Whitsunday, 

 commencing at the term of Martinmas 1847. And further, that the 

 Treasurer be required to report to the Philosophical Society at least once 

 every year the state of the fund, and that the Philosophical Society see 

 that this report to them is regularly given in." Which motion was 

 unanimously approved of by the Society. 



The two following papers were communicated by Dr. R. D. Thomson. 



XXX. — On the Chemical Composition of tlie Substances employed in 

 Pottery. By Mr. R. A. Couper. 



Most kinds of pottery arc composed of two parts, viz., the body 

 and the glaze. 



The body is the principal part of the vessel, being the base or founda- 

 tion, as indicated by the term itself. 



The glaze is a thin transparent layer of glass which covers the body 

 and fills up its pores, giving it a smooth surface, with a polished and a 

 finished appearance. 



I. The substances principally employed to form the body of earthen- 

 ware are, clays of different kinds, flint, and Cornish stone or granite. 



Clay, which constitutes the base of the body of earthenware, is dis- 

 tinguished from silicious earth by becoming plastic when mixed with 

 water, and being very soft and not gritty to the feel; also, when burned 

 it keeps its form, and becomes firm and solid, whereas silicious earths 

 < nmil'l. int.. a powder when burned. Clay, when intensely heated, as 



