To fulfil the need for satismfactory methods for the determination of tungsten over the range 0.002 to about 1 per cent. in titanium and its alloys, two absorptiometric procedures have been developed, and subsequently extended to the examination of zirconium and its alloys.A direct procedure, based on the yellow colour produced by the reaction of reduced tungsten with thiocya.nate ions, is suitable for the determination of tungsten from 0.05 to 1.6 per cent. in titanium and many of its alloys, and from 0.01 to 1.6 per cent. in zirconium and its alloys; larger amounts can be determined by using a smaller sample weight. The procedure is simple and rapid, and is also suitable for application on a routine basis. Vanadium and molybdenum interfere, and, when these metals exceed specified limits, the toluene-3 : 4-dithiol pmcedure is recommended.A procedure, which depends on the formation of a bluish green complex with toluene-3 : 4-dithiol, is applicable to the determination of tungsten in both titanium and zirconium-bearing materials over the range 0.002 to 0.8 per cent. Vanadium does not interfere, and interference by molybdenum is overcome by means of a preliminary sulphide separation.TUNGSTEN may be introduced into titanium, zirconium and their alloys either from the parent ores or by contamination from the tungsten electrodes that are frequently used in the arc-melting of evaluation buttons. Its presence is undesirable because of its considerable hardening effect ; further, in zirconium-bearing materials used in nuclear reactors, only small amounts of tungsten (below about 0.005 per cent,) can be tolerated because of its high neutron capture cross-section.The objective was the determination of tungsten in these materials over the range 0.002 to about 1 per cent.Colorimetric procedures based on the use of thiocyanatels2*s and toluene-3 : 4-dithiol (dithiol),4 commonly used for the determination of tungsten in steel, have been applied to the determination of tungsten in titanium metal,516 and these procedures are at present used in this laboratory.'In the thiocyanate p r ~c e d u r e , ~ the sample is dissolved in hydrochloric acid and, in order to obtain reproducible blank values, titaniium is completely reduced by boiling the solution with stannous chloride before the addition of thiocyanate. In this procedure, the small absorption of the yellow complex formed between reduced tungsten and thiocyanate ions is measured in the presence of a considerable absorption due to the deep violet colour of titanous chloride, and this limits its application to the determination of tungsten in amounts above about 0.1 per cent. Further, during dissolution in hydrochloric acid, which usually takes several hours, part hydrolysis of titanium sometimes occurs, which results in inconsistent blank values.In order to extend the application of the thiocyanate procedure, modifications to the published method5 were examined. Thew included the use of fluoroboric acid as a solvent ; it forms a green-coloured complex fluorotitanate with titan...
