the Substances emjjloyed in Pottery. 437 



also previously dried at 212°. There is a variety of other 

 clays obtained from these fields, which are of less value, and 

 need not be enumerated here, as they are similar in appear- 

 ance to those already noticed. 



5. Red or brown clay, which is very abundant in the neigh- 

 bourhood of Glasgow, is a surface clay, and contains a large 

 quantity of peroxide of iron, which gives it a deep brown 

 colour. It is of this clay that common black ware, flower- 

 pots, and red bricks are made, which do not require a 

 very high temperature, else they would fuse. The analysis 

 gave — 



Silica 49-44. 



Alumina 34-26 



Protoxide of iron .... 7*74 



Lime 1-48 



Magnesia ...... 1*94 



Water 5-14 



100-00 



6. Yellow clay is obtained from various parts of the country, 

 and is so called from possessing a yellow colour both before 

 and after being burned, owing to the presence of iron. 



By mixing sandy clay and red clay together, we gain an 

 artificial yellow clay, which is often employed. 



Yellow clay, as analysed by Mr. John Brown, was found to 

 contain — 



Silica 58-07 



Alumina 27-38 



Protoxide of iron .... 3-30 



Lime -50 



Water 10-30 



Magnesia ....... trace 



99-55 



7. Fire-clay is also very abundant in this country, and oc- 

 curs both on the surface and several fathoms under ground. 

 It is termed marl, and is used principally in potteries for ma- 

 king saggars or vessels for placing the ware previous to burn- 

 ing to protect them from the flame; and owing to its coarse 

 particles, which cause the body to be very porous, is well 

 adapted for strong heats: crucibles, or large pots for glass 

 works, in which the glass is fused, are also made from fire- 

 clay, as well as bricks known under the name of fire-brick. 

 This clay was analysed by Mr. John Brown, who obtained — 



