HISTORY OF CAEBON DISULPHIDE. 61 



way of their loss. This moment varies with the nature of the soil to 

 be treated. A clay soil, for instance, cannot realize favourable condi- 

 tions when it is saturated with water, or when it is cracked by drought. 

 On the contrary, a sandy soil, after a slight rain, is in favourable con- 

 dition. The most propitious moment is when the soil presents a 

 certain interior mobility and a great enough density on the surface. 

 In these conditions the vapour of carbon disulphide easily diffuses 

 around the roots, and remains imprisoned by the hard surface, which 

 forms a sort of envelope. Those advantageous conditions may be 

 realized artifically by injecting carbon disulphide into a very dry soil 

 and watering the surface soil, after having carefully plugged the holes. 

 (3) Never to stir the soil after treatment, for the carbon disulphide, 

 already very volatile, would, in certain instances, escape into the ajr 

 without producing its effect ; it is therefore necessary, so as to employ 

 it with success, to maintain it as long as possible in the infected zone. 

 To attain this end recourse has been had to two preparations, which 

 allow a less rapid evaporation of carbon disulphide. 



Vaselinated Sulphide. — In 1874 Bouttin proposed a mixture of 

 carbon disulphide and nut oil. Cubes of wood, imbibed with sulphide, 

 and covered with silicate of soda have been tried but neither of these 

 processes have given good results. Vaselinated sulphide was invented 

 in 1887 by Dr. A. Meunier and examined by Cazeneuve : vaseline forms 

 an emulsion with carbon disulphide and prevents it from evaporating 

 rapidly. It was hoped, owing thereto, to lessen the chances of evapora- 

 tion into the atmosphere and to prolong its action in the soil. Mixtures 

 were tried of equal parts of the two substances, or of 30 per cent of 

 vaseline and 70 per cent of carbon disulphide. In 1890, 250 metric 

 tons of these substances were used in viticulture. It has been observed 

 by Vermorel and Jossinet that the dose of 20 gi-ammes of liquid carbon 

 disulphide placed in each hole 35-40 centimetres round the vine suffices 

 to kill the phylloxera, but when mixed with vaseline this quantity is 

 not enough. However, if the holes be brought to within 10-15 centi- 

 metres of the stock, the conditions favourable to the action of this 

 preparation are improved. Marion and Gastine conclude that there 

 is no advantage in this mixture, since the dose of sulphide must be 

 greater to give the same result. They further remark : If more than 

 50 per cent of vaseline be incorporated in the carbon disulphide, the 

 evaporation which is produced during injection is as great as when 

 employed pure, and finally the vaseline retains about 15 per cent of 

 sulphide which it only cedes very slowly, and which remains without 

 effect. Wooden cubes impregnated with sulphide as well as mixtures 

 of carbon disulphide and heavy oils, tested by Marion and Gastine as 

 far back as 1877, gave no advantageous results, and the pure sulphide 

 should be preferred to all these preparations. It is a great error to 

 imagine that carbon disulphide must develop slowly to produce a 

 salutary effect. For the action of the sulphide to be effective, what is 

 required, above all, is to create almost instantaneously an atmosphere 

 highly charged with poisonous vapours around the radicular system 

 invaded by the parasites and to maintain it there as long as possible. 

 To slacken the evaporation of the carbon disulphide is to remove from 



