Amongst the earths, Silica or the earth of flints 5 

 probably consists of two proportions of oxygene to 

 one of silicum ; and Magnesia, Strontia, Baryta or 

 Barytes, Alumina, Zircona, Glusina, and Ittria of one 

 proportion of metal and one of oxygene. 



The metallic oxides in general consist of the metals 

 united to from one to four proportions of oxygene ; 

 and there are, in some cases, many different oxides of 

 the same metal ; thus there are three oxides of lead ; 

 the yellow oxide, or massicot, contains two proportions 

 of oxygene ; the red oxide, or minium, three ; and the 

 fuse coloured oxide four proportions. Again there are 

 two oxides of copper, the black and the orange ; the 

 black contains two proportions of oxygene, the 

 orange one. 



For pursuing such experiments on the composi- 

 tion of bodies as are connected with agricultural che- 

 mistry, a few only of the undecompounded substan- 

 ces are necessary ; and amongst the compounded 

 bodies, the common acids, the alkalies, and the earths, 

 are the most essential substances. The elements 

 found in vegetables, as has been stated in the intro- 

 ductory lecture, are very few. Oxygene, hydrogene, 

 and carbon constitute the greatest part of their organ- 

 ized matter. Azote, phosphorus, sulphur, mangane- 

 sum, iron, silicum, calcium, aluminum, and magne- 

 sium likewise, in different arrangements, enter into 

 their composition, or are found in the agents to which 

 they are exposed ; and these twelve undecompound- 

 ed substances are the elements, the study of which 

 is of the most importance to the agricultural chemist. 



