TJie Neglect of Ckemistry hy Practical Farmers. 429 



parts of tlie ash ; and in tlie other 3 parts it is the amount con- 

 tained in 100 parts, ton, &c., of the whole substance, in its natural 

 state. To prevent any mistake I have enclosed this column in 

 double lines. 



Sand and Silica. — The reason for placing sand and silica, instead 

 of silica alone, at the head of this columm, is, that a minute quan- 

 tity of extraneous dirt often adheres to the specimen, notwithstand- 

 ing all the precautions of the chemist ; and when the amount of 

 oxide of iron, as well as the silica, appears to be much above the 

 general average, it may confidently be referred to this cause, 

 althouofh there be nothins: recorded under the head of alumina^— 



O o .... 



for many chemists now never test the presence of alumina in plants, 

 from a belief that its presence is merely accidental. 



Silica, Silicic Acid, or pure Flint, is a white, inodorous, insipid 

 earth ; it is seen nearly pure in rock crystal, and in its ordinary 

 state is insoluble and infusible, but when combined with an 

 alkali, in certain proportions, is soluble, and in others fusible as 

 in common glass. The shining coat on the straw of cereals is 

 nothing but a species of glass. Silica is now often termed an 

 acid, on account of its similarity to the other acids, in its action 

 upon the alkalies and earths, destroying their corrosive property, 

 &c. The compound formed by its union v/ith any substance is 

 called a silicate of that substance. 



Potash, Soda. — These alkalies are so similar in their appear- 

 ance, that when in a state of purity it is quite impossible, by in- 

 spection, to distinguish one from the other ; but when in union 

 with the same acid the salts they form are very different, both in 

 appearance and properties. Their principal use in the arts is in 

 the manufacture of soap and glass. The potash and soda which 

 are so commonly used for domestic purposes are combined with 

 a variable small proportion of carbonic acid. 



The potash of commerce is procured chiefly from the burnt 

 ashes of plants, which fact of itself ought to be sufficient to im- 

 press upon the minds of farmers the identity between the consti- 

 tuents of plants and the same substances of commerce. Soda is 

 principally obtained from common salt, as also from kelp and 

 barilla. 



Lime. — The common lime used in agriculture is not quite pure, 

 as will appear by referring to the analyses of chalk and limestone 

 in these tables, but for all practical purposes it may be so consi- 

 dered, and its properties are so well known by farmers as to re- 

 quire no further description here. I may add, that slacked lime 

 is lime in combination with water, called by chemists hydrate of 

 lime ; and so great is the affinity of lime for water, that it has been 

 found by experiment that 1 ton of fresh-burnt lime increases daily 

 1 cw^t. in weight for the first five or six days, by the absorption 



