Mr. Couper on the Chemical Composition of Pottery. 173 



(3.) Pipe Clay is the second layer, which is used in making tobacco 

 pipes. This clay is not employed for manufacturing earthenware, owing 

 to its possessing the property of contracting more than sandy clay. It 

 was analysed by Mr. John Brown, who obtained — 



Silica, 5366 



Alumina, 3200 



Protoxide of iron, 1*35 



Lime, *40 



Maguesia, a trace. 



Water, '..1208 



90-40 



(4.) Blue Clay is of a greyish colour, and is considered the best layer 

 of clay in the whole series, owing to its burning perfectly white, and 

 approaching in character nearest to the China clay. As analysed by Mr. 

 John Higginbotham, it was found to consist of — 



Silica, 46-38 



Alumina, 3804 



Protoxide of iron, 1-04 



Lime, 120 



Magnesia, a trace. 



Water, 1357 



100-23 



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 appearance to those already noticed. 



(5.) Bed or Brown Clay, which is very abundant in the neighbourhood 

 of Glasgow, is a surface clay, and contains a large quantity of peroxide 

 pf 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- 



(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. 



