The development of methods for finding the equivalence volume by using linear regression methods is reviewed. The methods discussed are mainly those developed and used at the Department of Analytical Chemistry at the Royal Institute of Technology in Stockholm. No attempt has been made to cover the large number of methods of finding the equivalence volume in potentiometric titrations developed elsewhere.

Previous parts of this series have presented methods for the evaluation of titration data. This paper shows the utility of some of these methods and extensions of them for solving a practical problem, i.e., the determination of alkalinity and total carbonate in sea water. The procedure is based on the solution of a set of linear equations.The method presented has been tested on theoretical and experimental titration data and has given results that compare extremely well with those obtained by using non-linear curve-fitting methods.

A very simple method for numerical calculation of the equivalence volume (Ve) from titration data is presented. It is based on the method of stepwise addition of equal volumes of titrant combined with an extended version of the Gran I method.The expressions derived may be summarised in a general equation: [graphic omitted] where Vi and Vj are two additions of titrant (Vi is iVp, where Vp is the volume of each addition). The term aij is different for strong acids and weak acids and for conditional titrations, but in all instances only the ratio between hydrogen ion concentrations is required. E. g., for a weak acid [graphic omitted].The titration method can also be used for the determination of the conditional normal potential E′o and the constant jH in the junction potential jH[H] for an electrode couple in a given medium.

In the tin-- zirconium system, four intermediate phases are reported to exist, viz., Zr/sub 4/Sn, Zr/sub 5/Sn/sub 3/, ZrSn, and ZrSn/su b 2/; crystal structures are given for ZrSn/sub 2/ and Zr/sub 5/Sn/sub 3/. Alloys of several compositions were prepared from metallic zirconium and tin of 99.95% purity by melting pressed tablets of the metals in an electric arc furnace under argon. The samples were wrapped in tantalum foils, sealed in evacuated silica tubes, and annealed at 900 deg C for two months. An indexed powder pattern of ZrSn/sub 0.6/ containing two phases of Zr/sub 5/Sn/sub 3/ type is tabulated. At a composition ZrSn/sup 0.4/ the Guinier pattern showed, in addition to the pattern of the defective Zr/sub 5/Sn/sub 3/, a nunnber of strong extra lines. Assuming a cubic unit cell, the extra lines could be indexed with a = 5.634 A, which corresponds to the B-tungsten structure and which should be given the formula Zr/sub 3/Sn. (B.O.G.)

A new reaction for the spectrophotometric microdetermination of copper is described. To a strongly ammoniacal solution containing traces of copper is added a saturated solution of oxalyldihydrazide and formaldehyde or preferably acetaldehyde. A blue-violet to violet color of unusually high intensity is obtained. The absorbancy maximum is situated at about 542 mμ and the molar absorbancy index has a value of about 29,500 (logϵ = 4.47). This value is most certainly the highest hitherto known for any copper reagent..

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