430 TJte Neglect of Chemistry by Practical Farmers. 



of water from the atmosphere, a fact that may be of some prac- 

 tical importance for farmers to know. Gypsum is lime in com- 

 bination with sulphuric acid ; when burnt it is termed plaster of 

 Paris. Lime in combination with phosphoric acid forms the 

 principal ingredient in bones, so valuable as a manure. 



Magnesia — Is very similar both in appearance and properties 

 to the preceding when in its caustic state. The form of its salts, 

 however, is very different ; Epsom salts, for instance, doubtless 

 well known to most of my readers, is magnesia in union with 

 sulphuric acid, a very different salt from gypsum, mentioned 

 above. 



Alumina, or pure clay, is a colourless, insipid, insoluble pow- 

 der ; it has a strong attraction for moisture, which it rapidly ab- 

 sorbs, to the amount of one-third of its own weight. When mixed 

 with water it is characterized by the plasticity of the mixture. It 

 is soluble in most acids, and in alkaline solutions. In a crystal- 

 lized state it is seen in the sapphire, ruby, and topaz. Common 

 clay has, comparatively speaking, but a small amount of pure 

 alumina in its composition {vide Analysis). Alum is a com- 

 bination of alumina, potash, and sulphuric acid. 



Oxide of Iron, or rust of iron, occurs generally in the form of 

 protoxide ( black rust), or peroxide (red rust), but chemists generally 

 calculate its amount in the latter form, although Professor Johnston 

 has proved that it is present in soils in both forms. Green vitriol 

 is iron in combination with sulphuric acid. ' 



Oxide of Manganese. — There are five oxides of manganese, 

 although it is generally estimated by chemists as peroxide. From 

 all that is at present known on the subject, it does not appear to 

 possess much interest for farmers, its presence in those ashes where 

 it has hitherto been detected, being probably accidental. 



Chlorides of Potassium and Sodium. — These salts used formerly 

 to be termed muriates, but are so only when water is present, the 

 hydrogen of the water uniting with the chlorine, forming muriatic 

 acid, and the oxygen with the metals (potassium, &c.) forming 

 potash, &c. Chloride of sodium is pure dry common salt; the 

 salt in common use has a slight admixture of magnesia, &c. ( Vide 

 Analyses.) 



Chloride of potassium is sometimes found in rough saltpetre 

 (nitrate of potass), and is often taken for common salt. 



In some of the analyses the reader will observe that the amount 

 of chlorine only is given, and I had some idea of resolving the 

 chlorides into their simple elements, in order to reduce all the 

 analyses to one standard ; but, upon second thoughts, I determined 

 not to do so, principally on account of the interest attached to the 

 quantity of common salt contained in any plant. By the Table of 

 Chemical Equivalents appended to these explanations, the reader 



