GAS LIME. 171 



greatly extols the application of small quantities (up to ^cwt. 

 per acre) of ferrous sulphate as a top-dressing for meadows, 

 and also for beans, cabbages, potatoes, mangolds, and cereals. 

 He found that the iron sulphate increased the amount of 

 chlorophyll in the green portions of the plant, that the crops 

 were larger, richer in solid matter, albuminoids, and phos- 

 phates, and that the growth of mosses, &c., was hindered or 

 prevented. He also claims that the iron, to a certain extent, 

 performs the functions of potash in the plant, and that in many 

 cases ferrous sulphate may advantageously be substituted for 

 kainite or other potash manures. Continental experimenters 

 have confirmed in many instances the claims of ferrous sul- 

 phate as a manure. In addition to its specific action, it, like 

 other sulphates, probably supplies sulphur. 



Gas Lime. In the preparation of coal-gas various sulphur 

 compounds are expelled by distillation from the coal, and 

 though a considerable proportion of these are collected in the 

 ammonia-liquor and tar, some find their way into the gas, and 

 inasmuch as they are highly objectionable there, purification 

 has to be resorted to. One of the common methods of 

 removing sulphuretted hydrogen and carbon disulphide from 

 the coal gas is to pass it into chambers containing layers of 

 slaked lime, when the following reactions occur : 

 CaH A + H 2 S = CaS + 2H 2 



CaS + CS a = CaCS 8 . 

 Simultaneously, the carbon dioxide is also removed 



Small quantities of cyanogen are also absorbed. 



The spent lime is a complex mixture calcium sulphide, 

 sulpho-carbonate, sulphite, carbonate, thiocyanate, and hydrate 

 being the chief ingredients, with varying small quantities of 

 ammonia, cyanides, ferrocyanides, &c. Many of these com- 

 pounds are powerful plant poisons and fresh gas lime is 

 extremely destructive to all plant life. On exposure to air 

 and rain, especially if mixed with soil, absorption of oxygen 

 takes place, and the sulphides, sulphites, &c., are oxidised 

 first into thiosulphate and finally into sulphate 



