128 MASS. EXPERIMENT STATION BULLETIN 254 



Character of the Commercial Product 



From a chemical standpoint basic copper sulfate may be considered the active 

 principle which together with gypsum and excess lime compose Bordeaux. The 

 low basic sulfate prepared with calcium carbonate contains about 51+ per cent of 

 gypsum while the high basic sulfate prepared with basic magnesium carbonate or 

 sodium carbonate appears to be largely tribasic sulfate. Physically basic sulfate 

 is not as highly dispersed as Bordeaux and therefore has a lower power of suspen- 

 sion, distribution (coverage), adhesiveness and general effectiveness. From the 

 inception of the project the main objective was to prepare a Bordeaux substitute 

 that could be readily dispersed in water and was substantially as effective in con- 

 trolUng diseases on vegetables and fruits as Bordeaux, but not necessarily of the 

 same copper content. The use of basic sulfate as a dust has been of more recent 

 application. 



Since the Station laboratory is not equipped for quantity production, arrange- 

 ments have been made, from time to time, with different chemical manufacturers 

 to prepare basic copper sulfate for use in field work according to directions 

 furnished. The G. Chem. Co. prepared low basic sulfate with calcium carbonate 

 in 1925, two lots in 1926, and preliminary samples of high basic sulfate with basic 

 magnesium carbonate in 1927. The M. Chem. Co. prepared high basic sulfate 

 from sodium carbonate in 1927, and the C. Chem. Co. low and high basic sulfates 

 with calcium carbonate and sodium carbonate, respectively, in 1928. Several 

 manufacturers refused the work from lack of time, equipment or willingness to 

 undertake a new product. With adequate tank agitators, rapid filtering apparatus, 

 and other necessary equipment there does not seem to be any particular difficulty 

 in producing basic sulfate, but without such facilities secondary reactions are 

 likely to take place and more or less carbonate results. Furthermore, lack of 

 adequate faciUties generally injures the physical properties even more than the 

 chemical, which is particularly objectionable in the case of copper fungicides where 

 the size and character of the particles may be greater hmiting factors in disease 

 control than differences in composition. Basic sulfate, however, is generally 

 acknowledged as being more efficient than basic carbonate of the same degree of 

 dispersion. The absence of an appreciable amount of excess precipitant is to be 

 noted in both high and low basic sulfates, and of by-products in high basic sulfate. 

 The physical attributes sought are a soft, light, bulky, free-flowing product of 

 fine amorphous particles having a high power of suspension in water, highly sus- 

 tained air-floating properties as a dust, and good adherence to foliage and fruit. 

 These characteristics are seldom attained in entirety but are more fully reproduced 

 in the laboratory than in the factory in mass production. None of the firms 

 appeared to have all the equipment needed to perform the work according to 

 directions. The quality as a whole was rather inferior as judged by laboratory 

 standards. In^large measure the degree of dispersion is becoming recognized as 

 the criterion and in practice is generally determined by suspension. The seven 

 lots are summarized in Table 1. 



The copper content of the several samples of low basic sulfate was fairly con- 

 cordant and likewise those of the high basic sulfate. The amount of carbon 

 dioxide indicates the presence of comparatively little carbonate except in three 

 instances. As a whole the green-blue or light-blue lots seemed to be preferable to 

 the darker colored. Most samples were soft, bulky and free from grit and of 

 either a fibrous or powdery character. The fibrous samples were quite bulky 

 and contained well developed spicules of calcium sulfate which were produced 

 simultaneously with the basic sulfate and attached thereto, forming relatively 

 large particles which agglomerated readily but did not pack. When the conditions 



