ALUM. 163 



the mechanical action of the talc must play an important part in this 

 preparation, as Jean Burnat has obtained as excellent results as Baretto 

 with the following preparation which did not contain sulphate of 

 alumina : cement 20 per cent, soapstone 30 per cent, hydraulic lime 

 50 per cent. Burnat uses this mixture in copious powderings after 

 previously moistening the diseased vines with a solution of soft soap. 

 These two preparations are the only ones which, with that of Sokolnicki, 

 have given satisfactory results in the treatment of grey rot of the 

 vine. 



55. Alum, Al,3(SOJK.,S0^24H.,0. — Preparation. — Ordinary 

 alum is a double sulphate of alumina and potash. To prepare alum 

 pure clays are calcined in a reverberafcory furnace and then pulverized 

 and mixed with 40 per cent of sulphuric acid, 52' B. The mixture is 

 kept for several days at a temperature between 60° and 80° C, at the 

 end of which time the silica is deposited; the alumina is dissolved as 

 sulphate of alumina, which, decante 1 and mixed with sulphate of potash, 

 produces crystals of alum in the form of regular octahedra. 



Properties. — Alum is a colourless salt of a sweet and astringent 

 taste, much more soluble in hot water than in cold. Alum solutions 

 have a slight acid reaction. 



Action of Alum on Plants. — The vine does not stand this product 

 and dies if it be watered with a 5 per cent solution of alum (Mouille- 

 fert). 



Action of Alum on Fungi. — Kuhn examined in 1872 the action 

 of an alum solution on the diseases of cereals produced by the fungi 

 Ustilago and Tilletia. After fifteen hours' action on the spores some 

 were still capable of germinating. According to the laboratory tests 

 of Eavaz and Guirand aluminium sulphate has a decided action on 

 Botiytis cincrea. This action is more evident than that of blue vitriol, 

 which is almost nil ; whilst, according to Millardet, the spores of 

 Peronospora viticola are killed by a solution of 3 in 10,000,000, those 

 of Botrytis cinerea still develop in a solution of 3 in 1000 of blue vitriol. 



Action on Insects. — Alvood found that a 3 per cent solution and 

 even a 9 per cent solution does not kill cabbage grubs and lice. 

 Neither does it kill the larvae of the gooseben-y saw-fly, Nematus ven- 

 triculosus, Kl. 



Use. — Botrytis cincrea (grey rot of the vine). — Amongst the sub- 

 stances recommended to combat this fungus two preparations have been 

 recommended and given good results ; they both contain alum or sulphate 

 of alumina. Sokolnicki's contains 20 per cent alumed plaster [alumed 

 plaster is obtained by adding 10 per cent of alum to plaster beaten up 

 with water and reheating it], that of Baron de Chefdebien 3 per cent 

 of aluminium sulphate. [The composition of both these mixtures has 

 been given under calcium bisulphite and talc] The two compositions 

 were successfully used in Brazil and in the department of the Gironde, 

 and their efficacy is undoubted, yet De la Bathie got no result by using 

 a bouillie contaming 0-5 of alum or sulphate of alumina and a little lime. 



Schizoneura lanigera, Hausm. (woolly aphis). — Alum has been 

 advised and frequently used for a very long time to combat this louse. 

 Some results were got by a solution of 2 per cent alum and 4 per cent 



