Of the micro-methods which have been proposed for the determination of copper, the method of Biazzo (1926) as modified by Elvehjem and Lindow (1929) has been found to be the most practicable. Until recently McFarlane, (1932), the accuracy of this method has never been questioned. At this laboratory the method was found to give fairly satisfactory results when applied to biological material. In the cases of spleen and blood where the presence of excess iron, due to the large aliquots necessary, interfered with the colour development, the copper had to be separated from the iron at a carefully adjusted pH. The discovery by Callan and Henderson (1929) that when an aqueous solution of sodium-diethyldithiocarbamate is added to a solution containing copper, a golden brown colour is developed with the formation of a normal copper salt of diethyldithiocarbamic acid. This colour reaction forms the basis for the method discussed here am1 has lately found much favour in the colorimetric determination of copper.
MacFarlane (1932) extracted the colour quantitatively with amyl alcohol, thereby intensifying• the colour and increasing the sensitivity of the method. It was found necessary, on account of the great number of analyses to be done here, that a rapid and accurate method was estiential, and for this purpose the methods of MacFarlane (1932) and Tompsett (1934) were modified and applied as described here. A large numbe1: of copper determinations was Jolle by this method in conjunction with certain copper experiments at present in progress at Onderstepoort. These determinations were done on both normal and pathological post-mortem material as well as on several hundred grass and shrub samples. These results will be incorporated ill later publications from this
Institute, in a study on the role of copper in certain stock diseases.