GREEN VITRIOL. 171 



68. Sulphate of Iron, syn. Green Vitriol, FeSO^TH.p.— Pre= 

 paration. — (1) By roasting iron pyrites and lixiviating the product. 

 (2) By slow oxidation in the air of pyritic shale. (3) By dissolving 

 iron turnings [or scrap iron] in dilute sulphuric acid. By concentrating 

 the solution to 40° B., it abandons green crystals responding to the 

 formula FeSO^TH.p. 



Properties. — Solubility, 100 parts of crystallized green vitriol dis- 

 solved in 143 parts of water at 15° C, and in 30 parts of water at 

 ]00° C. To prepare solutions of green vitriol it is best to use boiling 

 water ; they must then be kept in closed vessels, for the salt is readily 

 converted into a slightly soluble basic sulphate of sesquioxide of 

 iron in contact with the air ; green vitriol has a styptic, astringent 

 taste. 



Action of Green Vitriol on Green Plants. — Iron is invariably 

 present in all green plants, but often in very small quantity. As to 

 its distribution in the plant, it may be said to be present more especially 

 in all the green parts, without being, however, entirely absent in 

 other parts of the plant. Iron may be considered as necessary to 

 plants as to man and animals. Its absence produces a pathological 

 condition known as cMorosis. Culture experiments have shown that 

 the plant cannot develop itself normally in absence of iron. The 

 necessary quantity is very small, and 2-5 milligrammes suffice for a 

 cereal plant (Knop). Sachs induced artificial chlorosis by cultivating 

 plants in a soil in which iron was excluded. Experiments made in 

 nutritive solutions show that the seed may germinate and the young 

 plant grow normally in the absence of iron ; the small quantity of iron 

 present in the seed amply suffices in the beginning to allow a normal 

 growth, but later on a fresh portion of iron becomes indispensable or 

 the plant gets into a bad state. Knop proved that the amount of iron 

 in a gland was sufficient to prevent chlorosis of the young oak for two 

 years. The plants which succeed best are those treated with a 0-15 per 

 cent solution of green vitriol ; a stronger dose than 0"2 per cent is often 

 injurious. The absence of green in plants deprived of iron has given 

 rise to the idea that iron takes part in the formation of that colour, but 

 we are far from knowing exactly what is its role in the formation of 

 chlorophyll. Formerly it was believed that iron entered into the com- 

 position of chlorophyll as in the hsemoglobin of the blood, but this 

 opinion is not entertained at the present time. The analysis of purified 

 chlorophyll and the demonstrations of Armand Gautier and Hoppe- 

 Seyler prove, in fact, that iron does not enter into the chemical composi- 

 tiou of the green parts of plants. Certain recent discoveries, however, 

 lead us to suppose that there exists along with chlorophyll substances 

 of analogous composition containing iron. Iron is not only indispens- 

 able to the normal formation of chlorophyll, but it has a favourable 

 action generally on the life of the plant. Green vitriol applied to the 

 surface of a green orange becomes yellow by the absence of iron salts and 

 restores to it its primitive colour. Brogniart, Gris, and Treviranus have 

 already described this and produced drawings made on the leaves to 

 show the local action of green vitriol. Millardet and Knop believe that 

 like blue vitriol gi-een vitriol acts without penetrating the leaf, for 



