EAU CELESTE. 265 



eau celeste than pure blue vitriol, which renders this treatment less 

 costly than those in use. There is, however, a third cause, which 

 explains the poisonous action of eau celeste on plants. "Whether pre- 

 pared with or without an excess of ammonia the eau celeste, in drying, 

 disengages ammonia on the surface of the organs attacked, and in 

 greater quantity the greater the excess of ammonia, Now, ammonia 

 is injurious to plants ; as soon as the air contains a doze exceeding 70 

 milligrammes per cubic metre of air, it causes bin-ns already described. 

 To replace bouillie bordelaise with advantage eau celeste should not 

 be made from more than 0-5 per cent of blue vitriol or 0-25 per cent 

 of copper carbonate nor with an excess of ammonia. To be certain 

 that an excess of ammonia has not been used it is well only to add 

 such an amount as will not entirely re-dissolve the precipitated copper 

 hj^drate. The chances of burning are thus much diminished. Be- 

 sides, it is well only to use eau celeste in fine dry weather, so as to let 

 the thin layer of liquid spread on the surface of the plant. To get an 

 eau celeste free from sulphate of ammonia this liquor is prepared as 

 follows (Prillieux) : Precipitate the blue vitriol as cupric hydrate with 

 half the quantity of ammonia used in making eau celeste; let this 

 celestial blue precipitate deposit ; decant the clear limpid supernatant 

 liquid, which contains all the sulphate of ammonia ; add water equal 

 in volume to the bulk of the liquid removed, and add the remainder 

 ■of the ammonia to dissolve the precipitate ; an eau celeste is thus ob- 

 tained which contains little or no sulphate of am monia. The same result 

 is obtained by adding to a 0'5 per cent bouillie bordelaise the ammonia 

 required to dissolve the precipitated cupric hydrate, then decanting 

 the dark blue supernatant limpid liquid after some time from the 

 deposit formed by the excess of lime and sulphate of lime. This eau 

 celeste no longer contains traces of sulphuric acid nor of sulphate. By 

 taking these .precautions in the preparation of eau celeste, and only 

 oisiag it rationally, this liquor is excellent, and especially cheap. A 

 drawback of eau celeste is that it leaves no decisive mark on the 

 leaves. Eau celeste is especially advised to combat cryptogamic 

 diseases in full evolution in circumstances where the use of bouillie 

 bordelaise would have no effect. In such cases its special properties, 

 its energetic action on the conidiophores and on spores, produce the 

 best results. Its corrosive action on the leaves in the dose required to 

 stop the first attack of fungi in the spring, will always cause it to be 

 inferior to neutral bouillie bordelaise, but in summer, when burns are 

 not to be feared, the second and third treatments for the year are 

 advantageously made with eau celeste. 



Eau celeste is, therefore, in the hands of the cultivator, a poiverful 

 agent for overcoming cryptogamic diseases in full evolution, whilst 

 bouillie bordelaise is par excellence the preventive remedy which should 

 protect the plant, by killing the germs tvhich are deposited on its sur- 

 face. 



Use. — The use of eau celeste has found numerous advocates in 

 France and Switzerland. Eau celeste modifice basin America in many 

 cases replaced bouillie bordelaise. 



Phytophthora infestans, De By. (potato disease). — Mohr advises to 



