802 EXPERIMENT STATION RECORD. 



per cent. For the purposes of comparison, the total nitrogen, the acid-soluble 

 iron and alumina, and the acid-soluble lime, are also given." " The maximum 

 quantity present in the soils examined Vv-as 0.59 per cent. The average of 

 seven soils rich in colloidal matter was 0.299 per cent inorganic colloidal ma- 

 terial." 



The average percentage composition of the inorganic colloids of the four 

 groups was as follows : Silica 59.7, 53.3, 51.5, and 47.5 per cent ; iron oxid 24.3, 

 12.6, 11, and 12.6 per cent; alumina 8.7, 16.9. 29.9, and 36.9 per cent; and 

 difference 7.3, 17.2, 7.6, and 3 per cent, respectively. " The most striking fact 

 about these averages is the decrease in percentage of silica, and the increase in 

 percentage of alumina, as the soluble colloid content of the soil increases." 



The molecular ratio of the constituents is: "0 to 0.05 per cent colloids — 

 l2SiO,:2Fe203: AI0O3; 0.051 to 0.1 i)er cent colloids— llSiO^ : 2Fe203 : 2AU.O3 ; 

 0.101 to 0.2 per cent colloids— 12SiO:: F2O3 : 4A1;03; 0.201 to 0.6 iier cent col- 

 loids— lOSiO^ : Fe^Os : 4A1:03." 



" In kaolin the ratio of silica to alumina is 2Si02 : AI2O3 : 2H2O. If we 

 assume that all the alumina is present as kaolin, then there is an excess of five- 

 sixths of the silica in the first group, seven-elevenths in the second group, one- 

 third of the silica in the third group, and one-fifth of the silica in the fourth 

 group. However, there were other bases present in the precipitate which were 

 not estimated. It api)ears probable that the soluble colloidal material [ex- 

 tracted by ammonia] consists of hydrated silica, hydrated oxids of iron, hy- 

 drated silicates of alumina with other bases, and possibly hydrated silicate 

 of alumina." 



Bordeaux mixture. — I, Physico-chemical studies, O. Butler (New Hamp- 

 shire Sta. Tech. BuL S (WU), PP- 125-180, pis. 2, figs. 3; Phytopathology, 4 

 (1914), No. 3, pp. 125-180, pis. 2, figs. 5).— There is apparently a marked di- 

 vergence of opinion regarding the composition of Bordeaux mixture, and accord- 

 ing to the literature it is clear that no agreement exists as regards the chemical 

 and physical properties (especially the latter). In consequence its toxic and 

 biological properties are also imi>erfectly understood. This paper deals with 

 the chemistry and physics of Bordeaux mixture. 



" Bordeaux mixture may be composed of one or several basic cupric sulphates 

 or mixtures of basic cupric sulphates depending on the ratio of ciipric sulphate 

 to calcic oxid employed. The copper precipitate of Bordeaux mixtures in which 

 the I'atio of cupric sulphate to calcic oxid is 1 : 1 or 1 : 0.5 becomes crystalline on 

 standing when the washes contain more than 0.125 per cent cupric sulphate. 

 The rate at which the copper precipitate becomes crystalline depends on the 

 temperature and concentration in cupric sulphate of the mixtures. The crystal- 

 lization of Bordeaux mixtures 1 : 1 and 1 : 0.5 is retarded by the presence of such 

 impurities as ferrous sulphate, calcic carbonate, magnesic oxid, and magnesic 

 carbonate; but this retardation is not due to the diluent action of the salts in 

 question. 



" The ci'j'stallizatiou of Bordeaux mixtures 1 : 1 and 1 : 0.5 may also be 

 delayed by various inorganic salts and organic substances, saccharose being 

 particularly effective. Bordeaux mixtures after carbonization are slightly 

 soluble in pure water, and dissolve readily in water containing carbon dioxid in 

 solution. Bordeaux mixtures are soluble in water containing ammonic salts in 

 solution. Alkaline Bordeaux mixtures are soluble in dextrose, saccharose, and 

 other organic substances giving the biuret reaction. The physical state of the 

 copper precipitate found in Bordeaux mixture is affected, irrespective of the 

 ratio of cupric sulphate to calcic oxid, by (a) the dilution of the salts and the 

 manner in which they are brought together; (b) the temperature of the water. 



