86 THE ANALYST. COPPER l C PURE FOR ANALYSIS.” BY JAMES W. WESTMORELAND, F.I.C., Associate of the Royul School of Miizes, London. (Read at the Meeting, February 2 , 1898.) SOME time ago circumstances which need not be detailed led me to examine a sample of copper-€oil, pure for analysis,” which had been obtained from a firm of wholesale chemists. The metal also contained *02 per cent. of lead, and some arsenic, but was not further examined. Later I called on the sellers, and found that their representative was by no means ready to admit the impurity of the metal; he stated that it had been supplied to many analysts, but none except myself had complained of the quality. Assuming this copper to be pure, and using it for standardizing volumetric solutions, it is evident that concordant yet very erroneous results might be obtained.For example, in testing material containing 5 per cent. of copper, the results would be 0.035 per cent. too high, with 70 per cent. material 049 per cent. too high, while metal con- taining over 99.3 per cent. would apparently contain over 100 per cent. copper. I next obtained some (‘ pure copper-foil ” from another dealer after requesting the assistant to be careful and give me the pure material. He pointed out the beautifully-planished surface of the metal as a guarantee of its purity, stating that such care would not be taken with ordinary copper-foil. The metal was well’ planished, but, as in many other cases, the outward appearance was no guarantee of inward purity. It is just possible that the vendor heard indirectly the result of this test, for mother sample purchased later was practically pure.I found it to contain copper, 99.30 per cent. It contained copper 99.10 per cent.THE ANALYST. 87 Another firm stated that their pure copper-foil was not electrolytic copper, but was probably nearly as pure, and this turned out to be the case. From another firm samples were obtained marked ‘‘ Copper-foil Opt,” which contained copper 99-81 per cent., and a sample of “ electrolytic copper,” prepared from purified sulphate of copper, which I have taken as one of my standard samples. From another London dealer I obtained some copper marked “Free from Arsenic ;” this is a specific1 statement of quality, but on examination I found the metal to contain : Copper ...... ... ... 99-23 per cent. Arsenic ... ... ... ... 0.67 ,, The following samples were obtained from a city in the North of Englend, marked Copper, pure for Analyses ” : ... ... ... ... 99-29 per cent. ... ... ... ... 99-64 ,, ... ... ... ... 99.87 ,, ... ... ... ... 99.03 per cent. ... ... ... ... 99.85 ,, ... ... ... ... 99.52 ,, ... ... ... .._ 99.65 ,, (4 Copper ( b ) ) 7 (4 7 7 (4 Copper ( e ) 7 8 (f> 2, (9) ), ( h ) 7 7 ... ... ... ... pure. 0 t her provincial samples gave Another sample, described I ‘ as pure as it is made,” contained copper 99.38 per cent, Another sample, marked ‘‘ Free from Arsenic,” contained copper 99.60 per cent., but was not further examined. I also obtained samples of metal which is sold as “ high conductivity copper,” and obtained the following results : (4 Copper ...... ... ... 99-86 per cent. ( b ) 9 ’ (4 9 7 ... ... ... ... 99.83 ,, ... ... ... ... 99.84 ,, I ’have used the electrolytic and iodide methods for determining the percentage of copper in the various samples. I t is evident that although samples which give 100 per cent. by the electrolytic test may possibly not be pure, samples which give lower results, say 99.5 per cent., cannot possibly be pure. The samples stated to be ‘‘ pure ” gave practically 100 per cent. by electrolytic test, and gave results agreeing within the error of experiment when used for standardizing thiosulphate solutions for the iodide test, in conjunction with copper obtained by the electrolysis of a solution of the pure sulphate, and of another sample of extremely pure copper, of which I obtained some quantity.Some of the impure samples were also used in this way (taking the percentage found by the electrolytic test)--and gave results agreeing within the limits of experimental error. ADDENDUM. Since my paper was read I have obtained two more samples of “electrolytic copper foil,” pure for analysis, from a London firm, whichcontained 99.00 and 99.09 per cent. of copper respectively.88 THE ANALYST. I have also obtained a sample of (‘ pure copper foil ” from a provincial dealer, which gave the following extraordinary results on analysis : Copper ... ... ... ... 94.42 Lead ... ... ... ... ... 0.39 Zinc ... ... ... ... ... 4.91 Iron ... ... ... ... ... 0.26 Arsenic traces ... ... ... ... 99 *98 I submitted a sample of this metal to a firm of London metal workers, who informed me that it was ‘‘pure Bright rolled copper.” The vendor, in answer to inquiries, stated that the metal was obtained some time ago from a London dealer, and that it was marked ‘‘ Electrolytic copper foil-pure for analysis-free from arsenic.” DISCUSSION. Mr. BLOUNT said that copper was a substance pre-eminently easy to obtain in a state of purity almost absolute. Nevertheless, the figures obtained by Mr. West- moreland showed a condition very far removed from purity. At the same time, although this indictment lay against copper sold as (‘ pure for analysis,” he could not help thinking that Mr. Westmoreland must have been a little unfortunate in his samples. Copper containing 99.1 or 99.3 per cent.of actual Cu, and sold as pure, was surely a somewhat unusual material, when it was considered that ordinary loco- motive firebox copper contained 99& per cent.-that was to say, it was not only specified to contain, but actually did contain, that quantity, and very often considerably more. He thought it would be interesting to know what was the balance of the impurities in each case. For instance, in the first sample referred to in the paper, containing 99.3 per cent., Mr. Westmoreland had found some arsenic, but had not said how much, or of what the balance consisted. Beside the arsenic, there was presumably something else. The percentage of arsenic found in the sample sold as ‘‘ free from arsenic,” viz., 0.67, was enormous in a refined tough copper, but even in this case a balance of 0.1 per cent.remained unaccounted for. I t seemed curious that so many of these arsenical coppers consisted mainly of copper and arsenic, being tolerably free from other impurities. Ordinary tough-pitch copper, containing 99.5 per cent. of actual Cu, and perhaps 0.2 per cent. of lead, would contain possibly 0.15 per cent. of arsenic, At the other end of the scale there might be 0.4 of arsenic, with 99.5 per cent. of Cu, all the other impurities being included in the remaining 0.1. It was just conceivable that some of the samples examined by Mr. Westmoreland were refined but not toughened coppers, and in such case they might very well have been free from most impurities save oxygen, It was impossible, however, to roll into foil copper containing much oxygen, so it seemed fair to assume that foil was not ‘( refined ” as distinct from ‘‘ tough-pitch.” The largest quantity of oxygen that could be contained by copper-foil would be about 0.15 or 0.2 per cent., so that the balance left from this and the actual Cu found by Mr.Westmoreland would probably be lead, arsenic, nickel (a common impurity in commercial copper), and the other odds and ends of things generally found. Touching the question of analysis, it was clearlyTHE; ANALYST. 89 evident that to obtain reliable results one must either be prepared to isolate the whole of the copper (and he knew of no process of doing this with any degree of accuracy except electrolysis), or one must have a standard for coinparison which was unexcep- tionable.He gathered that Mr. Westmoreland had followed both modes of pro- cedure, and in that case his figures would be gratefully received. He might mention, however, that in the electrolytic method it was necessary, in order to avoid serious errors, to isolate the copper as nearly as possible from a large quantity, e.g., 10 gramnies of the sample, and then to determine the residual copper in the solution. Mr. WESTMORELAND said in reply that, with the exception of one sample of electrolytic copper prepared from the pure sulphate and the three samples of L c high conductivity ” copper wire, all the samples were copper-foil. The samples were obtained from practically every dealer in the United Kingdom. His (Mr. Westmore- land’s) primary object was to obtain pure copper for standardizing volumetric solu- tions; consequently he had not troubled in most cases to further examine samples when he found they were impure. The absence of other impurities in arsenical coppers containing, as Mr. Blount suggested, 99.5 per cent. of copper and 0.4 per cent. of arsenic, may be explained on the assuniption that they are produced from very arsenical blister copper, and that, consequently, the other impurities present are eliminated before the arsenic is reduced to an allowable percentage. E e (Mr. West- moreland) had many years ago pointed out the necessity of determining the residual copper in the solutions from electrolytic assays.