Robert Law and His Auxiliary Assay Balance

In 1896, Robert Law, assayer at the Melbourne Branch of the Royal Mint, published a design for an auxiliary assay balance. This small balance was to be used for preliminary weighing of the gold sample, thus saving wear on the delicate assay balance. Versions of Law balances, including one made by the UK instrument firm of Oertling, were used in all Australian Branches of the Royal Mint, and two surviving instruments have now been found.

X-Ray-Induced Photoelectron Spectroscopy of Dentin as a Function of Duration of Ar +-Ion Etching

XPS, or ESCA, measures the atomic concentration in the outermost layers of the sample. The surface is often etched with Ar+-ions before any measurement. We investigated the role thereof on XPS measurements of root dentin. Nine slices were cut from premolars. Slices were ground or broken. XPS was measured before etching. Six samples were then subjected to Ar+-ion etching (10 kV ions, 0.25 μA/mm2). A gold sample was also included. Relative concentrations of N and C decreased with etching time, while 0, P, and Ca increased. N and C curves were analyzed assuming a sum of two exponential decays and a final level. On average, τ1 = 20 sec for C and 17 sec for N. On average, τ2 = 278 sec for C and 350 sec for N. No differences between differently prepared samples were apparent. The gold sample showed a single decay to noise for C and N, with τ1 = 8 and 7 sec, respectively. We conclude that two decay processes are present, due to gas removal and to the removal of organic material from the dentin matrix, respectively. Thus, true values can be obtained by extrapolation to t = 0 of only the data obtained by summing the slow decay and the final level.

Absolute Disintegration Rate of Finite Gold Sample: Determination by Coincidence Techniques

A method has been developed for absolute disintegration rate determination of finite-sized, radioactive samples. Measurements were made on a 15-mg gold foil. The average disintegration rate was 2.163X105 for 24 determinations with a precision of 2.3%. Subsequent measurements yielded precisions as low as 0.5%. Conditions of bias settings, decay corrections, and coincidence resolving times were widely varied. The scintillation, coincidence equipment, including novel pulse timing, are mentioned. Data corrections, including accidentals and particle A in detector B are discussed. It is shown that the corrections are empirical and do not limit the absolute nature of the measurements. Some of the nuclear parameter requirements and spectroscopic implications are indicated.

Polarographic Determination of Traces of Gold in Blood and Serum

A polarographic method for the determination of as little as 1 µg. of gold in blood and serum samples is described. The relative error is 2.1%. After the sample is dry ashed at 550°, the gold is extracted into ether as the chloride, to separate it from interfering copper and iron. A polarogram of the gold sample is obtained in 2 M potassium hydroxide. The method should be applicable to the determination of gold in other biological samples containing interfering elements.