absolute measure is 6,580,000 × 1999, or 1,316,000. The various results reduced to specific resistances per grain of mass per foot of length are collected in the following Table, and shown in order of quality in connexion with four determinations of specific conductivity by Weber.

Specific Conductivities of specimens of Copper expressed in British Absolute Measure.

Description of Metal.

Specific resistances.

Copper wire A No. 22 [=1853 C. G. S.]

7,600,000

Wire of electrolytically precipitated copper: Weber (1)

7,924,000

Copper wire B No. 22 [=1936 C. G. S.]

7,940,000

ART. LXXIX. ANALYTICAL AND SYNTHETICAL ATTEMPTS TO ASCERTAIN THE CAUSE OF THE DIFFERENCES OF ELECTRIC CONDUCTIVITY DISCOVERED IN WIRES OF NEARLY

PURE

COPPER.

[From the Proceedings of the Royal Society, February, 1860.]

FIVE specimens of copper wire No. 22 gauge, out of a large number which had been put into my hands by the Gutta Percha Company to be tested for electric conductivity, were chosen as having their conductivities in proportion to the following widely different numbers, 42, 71-3, 847, 86'4, and 102; and were subjected to a most careful chemical analysis by Professor Hofmann, who at my request kindly undertook and carried out what proved to be a most troublesome investigation. The following report contains a statement of the results at which he arrived :

"Royal College of Chemistry, March 10th, 1858.

"SIR, I now beg to communicate to you the results obtained in the analysis of the several varieties of copper wire intended for the use of the Transatlantic Telegraph Company, which you forwarded to me for examination,

"I have limited the inquiry to a minute qualitative analysis of the wires, to a very accurate determination of the amount of copper, and an approximative determination of the amount of oxygen. The qualitative analysis has been repeated several times with as considerable quantities as the amount of material at my disposal permitted. The quantitative determinations of the copper have been made with particular care, and after a lengthened scrupulous inquiry into the limit of accuracy of which the method employed is capable, I am convinced that the true per-centages of copper cannot be more than 0.1 per cent. either above or below the means of the determinations, the details of which I give you in the Appendix.

"The following Table contains the results furnished by analysis :—

Qualitative analysis Nickel. Nickel. Nickel (doubtful). Nickel (doubtful). Oxygen.

Arsenic. Oxygen. Oxygen.

Oxygen.

Oxygen.

Since it appeared probable that the extraordinary difference in the conductivity of the several specimens was due rather to nonmetallic impurities than to metallic admixtures, careful experiments were made in every case for the detection of sulphur. In none of the specimens was it possible to discover the slightest trace of sulphur. Qualitative experiments having established on the other

* I have since found [see preceding Art. LXXVIII. foot note pp. 115, 116.] 10-9 × 1311⁄2 as the factor to reduce from this to absolute measure. Thus the conductivities of the five specimens are respectively 55.2, 95.3, 111·4, 113·6, 134·1, in terms of one one thousand millionth of the British absolute unit.-W. T,

hand the presence of oxygen, probably in the form of suboxide of copper, in every one of the specimens, an attempt was made to ascertain the quantities by determining the loss which the wire after rolling suffered when heated in an atmosphere of hydrogen, and by simultaneously estimating the quantity of water formed.

"In this experiment, the details of which are given in its Appendix, the following numbers were obtained :—

Conductivity.......

Percentage of Oxygen

Unfortunately the same reliance cannot be placed upon these numbers as upon the preceding ones, since the method employed involves many sources of error, and want of material precluded the possibility of repeating the experiments.

"From the preceding analysis, it is obvious that the amount of impurities in the several specimens examined is small, varying as it does between 0·10 and 1·24 per cent. The number of foreign constituents also is comparatively small. I should, however, state that the analytical results which I have given do not exclude the presence of exceedingly minute quantities, even of other metals which might have been detected if larger quantities of copper could have been submitted to analysis. Some years ago, Max Duke of Leuchtenberg* examined the black precipitate formed at the anode in the electrotype process, during the decomposition of sulphate of copper by the galvanic current. In this precipitate, of which considerable quantities accumulate by the gradual solution of large quantities of copper passing through the process, he found the following constituents:

"Of these constituents, the ten first metals were obviously derived from the copper, in which they could have been scarcely detected unless by this accumulative process. Of the remainder of the constituents, the tin in a great measure is derived from the solderings.

"The results obtained in the analysis of the copper wires which you forwarded to me, appear to establish one fact in a satisfactory manner, viz. that the diminution of conductivity observed in certain specimens of copper is due to the presence in these specimens of a certain amount of foreign matter, and not, as it has been supposed, to a peculiar change in the physical condition of the metal; for in the specimens analysed the conductive power rises in the same order as the total amount of impurities diminishes.

(Signed)

"I have, &c.,

Professor William Thomson, F.R.S., &c."

"A. W. HOFMANN."

It appears therefore that in the case of these four specimens, the electric conductivity is in order of purity of the copper; but yet that only extremely small admixtures of other substances are to be found even in those which have but half the conductivity of the best.

On the other hand, I have found by experimenting on artificial alloys, that comparatively large admixtures of lead, iron, silver, and zinc seem to produce sometimes improvement, sometimes little or no sensible influence, and sometimes (as in the case of zinc) an injurious effect on the conductivity of specimens of pure electrotype copper from which the alloys were made. The largeness of the proportion of other metal required to produce any considerable deterioration in comparison with that of the whole amount of impurities which Professor Hofmann's investigation demonstrates in specimens of low quality as to conductivity, is worthy of remark, and seems to indicate that this low quality must be due to other than metallic impurities.

The great difference between the conducting qualities of two specimens of electrotype copper, from which two series of alloys were separately prepared, seems also to indicate some as yet undiscovered cause, as operative in general. I am assured by Messrs. Matthey and Johnson, by whom all the alloys were prepared, that similar methods were followed and equal care bestowed to ensure purity in the two cases.

The results of my measurements of conductivity are shown in the following Tables: