No. II.

MEMORANDUM BY MR. ROBERTS, F.R.S., CHEMIST OF THE MINT.

I append a statement of the number of assays made in my Office from the 1st of January to the 31st of December 1878 :

The total number of assays made during the preceding year was 6,719.

The duty of assaying a certain number of the gold coins struck at Sydney and Melbourne has, as heretofore, devolved upon my office, and the results prove that the coins issued from these Mints approximate in a remarkable manner to the exact standard of fineness. The average composition of the Pyx coins of the Mints at Calcutta and Bombay, received from the India Office, was also found to be satisfactory. The coins submitted to me from the Imperial Japanese Mint at Osaka well sustain the reputation of the European and native officers who are responsible for their production, and show that the Japanese Government is fully sensible of the importance of coining with accuracy.

ADJUSTMENT OF BLANKS.

Attention has been directed in former Reports* to a process proposed by me in 1870 for adjusting blanks by means of suitable solvents aided by a battery. It was found that the plan could not be adopted with profit in the Mint in this country, as the finished coin alone is weighed. In the Indian Mints and on the Continent it is very generally the practice to weigh the blanks, and it may be interesting therefore to mention that certain experiments on this subject, commenced in 1873 by Mr. S. L. Hynes and continued recently by Mr. F. W. Peterson, both of the Bombay Mint, have been attended with very successful results. The above-named officers have greatly extended the process by transferring metal dissolved from the rouleau of heavy silver blanks to a rouleau of light blanks, the whole being by this means brought to the prescribed weight. Mr. Peterson, who has studied with much care the conditions which affect the uniform solution and deposition of the metal, considers that the battery employed in the earlier experiments may be replaced with advantage by a small magneto-electric machine, and there

* First Annual Report (1870), pp. 42 and 110; and Fifth Annual Report (1874),

is every prospect that the process, which has already been employed on a large scale, will soon take its place in India as an ordinary operation of minting. Should this prove to be possible a considerable saving will of course be effected.

COUNTERFEIT COINING.

The two cases during the past year in which I was called upon to give scientific evidence are of some importance, and present unusual features. In December last a jeweller, named Hedges, was committed for trial at Maidstone, and subsequently convicted, on the charge of uttering counterfeit sovereigns and of having in his possession certain appliances suitable for making the counterfeits, which proved to have been cast in brass and electro-gilt. Such counterfeits are seldom met with, as the high melting point of this alloy renders it difficult, if not impossible, to produce them in the moulds usually employed.

In the second case a foreigner was found guilty at Liverpool of passing sovereigns which had been fraudulently reduced in weight by about five grains. It was evident that the "milling" of the coins in question had been very skilfully tampered with, and the case is important on account of the authoritative decision as to the meaning of the word "counterfeit " to which it has led.

DENSITY OF ALLOYS OF GOLD AND COPPER.

The results of experiments made last year on the density of discs of fine and standard gold showed that compression between dies raises their densities by 0 037 and 0 164 respectively. The effect of annealing the compressed discs at a red heat was to lower the density of fine gold by 0.013, and of standard gold by 0.032. The experiments on gold have since been contin: ed by Mr. Rigg with a view to ascertain whether the effect of rolling differs from that of compression between dies, the results hitherto obtained in the case of copper having proved to be somewhat contradictory.*

A fine gold ingot 8 mm. thick was rolled by successive stages to 0.23 mm. The mean of several results showed that the density of the cast metal was 19.294, and that there is a gradual increase to 19.340 at a thickness of 0.74 mm.; when reduced below this point the density appeared to remain unaltered.

The initial density of an ingot containing 92.7 per cent. of gold and 7.3 per cent. of copper was found to be 17.687, and rolling without annealing to half its thickness (from 7.8 to 4.19 mm.) increased the density to 17 704. The metal was now divided into two equal parts, one of which was rolled to a thickness of 1.12 mm., and, as its density was found to be 17.713, it will be evident that the volume of the metal can only be very slightly altered by rolling after it has passed a few times between the rolls. The strip was annealed at a dull red heat, and its density remained unchanged. On annealing the remaining half of the ingot in a similar manner, its density was also found to be invariable, but after prolonged annealing in red-hot charcoal it was much reduced, an effect found to be due to a molecular change in the metal, which rendered it crystalline and brittle.

NOTES FROM FOREIGN Sources.

Experiments on the Flow of Solids.

The relation which the raised portions of the obverse of a coin should bear to those on the reverse, though of much importance, is often neg

Sir W. Thomson, article " Elasticity," Ency. Britt., ninth edition, quoted in Eighth Annual Report (1877), p. 44.

lected by artists, and sometimes by skilful engravers, whose designs on separate dies are, in consequence, imperfectly represented or even distorted when the dies are employed simultaneously to produce impressions on the two sides of a metallic disc. As any theoretical facts which bear directly on this question must be of much practical value in coinage, I may perhaps be permitted to direct attention to some recent experiments by M. Tresca, sous-Directeur du Conservatoire des Arts et Métiers of Paris, on the "flow of solids." He has shown* that, when metals are submitted to compression, they so closely resemble fluids in their behaviour that the shape they will assume can be deduced by calculation. It is even possible to lay down the trajectory of the molecules of the compressed metal, and to establish with certainty the final places they will occupy as compared with their initial positions; it follows, therefore, that the final position of any line or surface may be predicted. In stamping, the pressure is found to be gradually transmitted from one zone or layer of the blank to another, in absolutely the same manner as in the flow of liquids, and with a regularity not less remarkable, although following a much more rapid law of diminution. The engraved work on the die forms in fact a series of channels designed to facilitate the flow of the metal of which the coin or medal consists, and to guide it in the required directions. In the compression of a blank between dies, the portions not to be brought into relief by the action of the press are reduced in thickness for the benefit of the neighbouring raised portions, the metal literally flowing radially from the level parts to the reliefs. This flow is of course gradual, and the presence of scars sometimes seen on medals in high relief may be traced to the junction, during the later strokes of the press, of projections formed in the earlier stages. With such facts in view, M. Tresca has shown that it may sometimes be useful to distribute the flow of the metal by centripetal instead of vertical compression. It is to be hoped that these experiments will be continued, as the results appear to afford a scientific basis for an art which must always depend greatly on technical skill and individual experience.

Paris Exhibition.

As regards design applied to coinage, the Exhibition, more especially the French section, was both instructive and interesting. The remarkable portrait medals by Ponscarme, the clever treatment of modern portraits and subjects, in imitation of Greek coins, by Zwillau, and the admirable works by Dupuis, which resemble early Italian cast medals, deserve the highest praise, and the collection as a whole proves the existence in France of a vigorous school of medallic art.

The influence of the chemical composition of steel on its resistance is a question of so much importance in relation to the preparation of dies, that such records of experiments as the Exhibition contained were of special interest.

The iron-works of Reschitza in Hungary exhibited curves and photographs recording the results of trials conducted by Prof. Bauschinger as to the compression, traction, flexure, shearing, and torsion of different varieties of steel. Similar results were published by the Swedish Comptoir des Forges, and by the Terre-Noire Company. The results of these trials have since been discussed in a very valuable and elaborate paper by

Paper read before the Society of Mechanical Engineers, Paris. Translated in the Journal of the Franklin Institute, Philadelphia, 1878, vol. lxxvi., pp. 263, 326, and 396.

M. V. Deshayes,* engineer of the latter company, who shows, from the experiments on impact and traction, that steels which oppose a comparatively high resistance when submitted to traction and contain from 0 6 to 0.7 per cent. of carbon, also resist impact very perfectly, and the same may be said as regards steels containing 0.8 to 10 per cent. of manganese and only traces of carbon. He further considers at great length the effects of various impurities on the several physical properties of steel.

Mechanical operations are not directly connected with my Department, but I may state, as the result of a careful examination of the various classes in the Paris Exhibition, that, although the improvement in design of machinery generally in recent years is very marked, there is but little evidence of advance in the appliances used for coinage. The well-known applications of friction gearing for transmitting motion to medal presses, shown by M. A. Bidault, and the movable furnaces exhibited by M A. Piat deserve, however, to be specially mentioned. In these furnaces the portion which contains the crucible may be detached from the flue so as to admit of the molten metal being poured into moulds without the removal of the crucible from the incandescent fuel. The various fittings are very ingenious, and the method well deserves trial in Mints; its use is stated to effect considerable economy in labour, fuel, and crucibles, and to possess many incidental advantages.

RESEARCH IN PROGRESS.

Considerable progress has been made in the investigation, commenced last year, with the view to extend the researches of the late Mr. Graham on the transpiration of liquids to the passage of molten metals and alloys through capillary tubes, and a preliminary report on the subject has already been submitted to the Royal Society. It was found that, when tubes with the finest bores that could be produced by a skilful tobaccopipe maker are employed, the flow of mercury takes place in accordance with Torricelli's well-known law, so that it was open to question whether the numerous results obtained on molten alloys of lead and tin could be considered to be of the nature of true transpiration. Subsequent experiments showed that a tube 600 mm. long, with a bore 0·4 mm. in diameter, causes mercury to obey the transpiration law of Poiseuille. It thus became necessary to devise a means of producing clay tubes of less than half the diameter of the finest that can be formed by ordinary means. Since the close of the year the difficulty of manipulation has, it is hoped, been overcome, and, as tubes of almost any degree of fineness can now be made, the experiments will at once be resumed.

3rd March 1879.

W. CHANDLER ROBERTS,
Chemist of the Mint.

* Bull. Chim. Soc. Paris, 1879, t. xxxi. pp. 166-186 and 205-227.

Profit on silver bullion purchased in the year for
coinage (as per Account, page 42)

Cost of alloy metal for gold coinage

Nil.

Loss on gold coinage (waste, partially recoverable in

the sweepings)

5,677 15 6

Loss on worn silver coin exchanged (as per Ac

Excess of expenses over receipts in the year ended 31st December 1878