Compounds free from sulphur and rich in arsenic, containing more arsenic than is necessary for the formation of Co,As and Ni,As, do not require roasting and arsenizing. Alloys (argentan, nickel coins, nickeliferous black copper, etc.) must be laminated, and several times arsenized with an equal quantity of arsenic; and also substances rich in cobalt (for instance, mixtures of nickel and cobalt oxides), which may have been precipitated in the wet way.

4. Reducing and solvent fusion for the purpose of collecting the metallic arsenides into a button (arsenical iron, arsenical nickel, arsenical cobalt), and of slagging off earths and foreign oxides, zinc being entirely, and antimony partly volatilized in the operation. The mass is placed in a sound crucible, and 10 to 12.5 grammes (154.32 to 192.90 grains) of potassium carbonate and flour are added to it. Upon this come a small spoonful of borax and two of powdered glass, and a covering of common salt with a small piece of coal. The crucible is then placed in the muffle-furnace, wood-charcoal is piled high around it, the mouth of the muffle is closed, and the charge, after the "flaming" has ceased, is fused for onehalf to three-quarters of an hour at an orange-red heat. The assay is then taken out, allowed to cool off, and the brittle button very carefully freed from slag.

Modifications which may occur :

a. Addition of iron filings: 0.5 to 0.75 gramme (7.71 to 11.57 grains) of iron filings must be added during arsenizing, if the ores, etc., are rich in cobalt, and refractory; 0.05 to 0.20 gramme (0.77 to 3.08 grains), if they are entirely free from iron, or contain but little of it, in order to prevent the slagging off of cobalt too soon, by the borax. If lead is present, 0.5 to 0.75 gramme (7.71 to 11.57 grains) of iron in the form of a thick wire are added, or the mass is fused in an iron crucible, which will allow a better regulation of the consumption of iron. The lead attaches itself upon the button of arsenides, and its weight is found by weighing lead and button together, cutting the former off and reweighing. If bismuth is present, it would attach itself upon the brittle button of arsenides, in the form of brittle metal,

which could not be detached from it. In this case, it is necessary to add 0.5 to 0.6 gramine (7.71 to 9.26 grains) of granulated lead to the charge, when a ductile alloy of both metals will separate on the button of arsenides, which can be easily disconnected from it. The approximate percentage of bismuth can be calculated after deducting the added granulated lead, minus 4 per cent. loss.

b. Arsenizing and fusing in one operation.-The roasted assay sample is rubbed together with arsenic in the same manner as previously stated, and the mixture is wrapped up in a cylinder of soda paper. The cylinder is formed over a wooden stick of 16 millimeters (0.63 inch) diameter, by closing the lapping edges with lac. It is pressed firmly into a crucible (Fig. 42, p. 64) and covered with 15 grammes (231.48 grains) of black flux, 1 small spoonful of borax, 1 small spoonful of glass, 15 grammes (231.48 grains) of common salt, and a small piece of charcoal. Accurate results are obtained by this process. Or, the roasted sample is rubbed together with an equal quantity of arsenic and 15 per cent. of arsenical iron (Fe,As), and fused with the above fluxes.

5. Slagging off of the arsenical iron.-Wood charcoal is placed all about the inside of the muffle, and one or two refining dishes are placed in the centre of it. The muffle is then closed, and the dishes are brought to a white heat by a strong fire. 1.5 to 2 grammes (23.15 to 30.87 grains) of borax glass are then placed in the dishes by means of an iron spoon (or wrapped up in a cornet), the muffle is closed and the borax fused. The button of arsenides is now placed in the dish, the mouth of the muffle is again closed, and the button fused as quickly as possible at a very high temperature (if the temperature is too low and the fusing takes too much time, cobalt also will be slagged off). The mouth of the muffle is now opened, placing a piece of glowing charcoal in front, to allow the entrance of air, whereby the arsenide of iron is oxidized to basic iron arseniate. This covers the button with a crust or scale (the scaling of the button) which is continuously dissolved by the borax until the

surface of the dull button appears bright, when this operation is finished. The dish is lifted out by means of the tongs, and the lower part of it is first dipped into water until its contents has ceased to glow, when the entire dish is submerged. The following are indications of a successful assay: The button is bright, the slag black or green, with a bluish tint, which is a sure indication of all the iron having been removed.

Modifications.—If the button is very rich in iron it is repeatedly treated with fresh borax, as this is saturated and becomes stiff and the button no longer "drives."

Separation of copper-red scales of iron arseniate from strongly saturated borax. More cobalt will slag off (the slag has a strong blue tint) if the temperature is too low or the slagging off is continued too long, or when no iron, or but little of it, was present in the button.

6. Dearsenizing.-An excess of arsenic is volatilized by heating the button in a small covered crucible (Fig. 39, p. 66) in charcoal powder, in the muffle heated to bright redness for one-fourth to one-half hour, in order that constant combinations of Ni,As and Co, As shall be formed. The resulting button is weighed, and the operation is repeated until its weight remains constant.

7. Slagging off the cobalt arsenide.-The process is the same as in slagging off the iron arsenide (p. 185), but at a higher temperature, the quiet button remaining bright during the slagging off of the cobalt. The process is interrupted as soon as a film of apple-green basic nickel arseniate forms on the surface of the button. The dish is taken and cooled off in the same manner as in the slagging off of iron arsenide (p. 185). If the assay has been properly done, the bright, white button will show on its surface small green patches of nickel arseniate, the slag is blue with a violet tint (from the blue of the cobalt and the brown of the nickel), and a green stain will be per

ceptible on the place where the button has rested. The button consisting of Ni,As is weighed, and the percentage of nickel calculated therefrom (p. 182), the Co,As being determined from the difference of Co,As+ Ni2AS2. B. Cupriferous compounds.

A percentage of copper' remains behind with Ni,As as a constant combination of Cu, As, and can be determined according to Plattner's method:

1. If the percentage of copper is small, and does not exceed that of nickel, by the addition to the weighed button (NiAs+ Cu,As) of 6 to 8 times the quantity of gold accurately weighed (to prevent a slagging off of the copper in the subsequent operation). The arsenide button with gold addition wrapped in a cornet is placed in salt of phosphorus which has been fused in a suitable shallow dish. This salt exerts a more vigorous effect than borax in slagging off with yellowish-brown color the nickel arseniate which will be formed. If necessary, the oxidizing process is continued by renewing the saturated salt of phosphorus until the button appears bright, a proof that the nickel is slagged off, the complete volatilization of the arsenic being indicated later on by the button ceasing to fume. The remaining alloy of Au and Cu is weighed, and the weight of the copper, which is obtained by deducting that of the added gold, is calculated to Cu,As, with 71.7 per cent. Cu, and deducted from the total weight of the Ni,As+Cu,As, from which the percentage of nickel is calculated.

This assay becomes less accurate with an increase in the percentage of copper, as, during the slagging off of the last portions of the nickel arseniate, the copper also commences to slag off. For this reason

B. u. h. Ztg. 1868, p. 24; 1868, p. 94 (Kleinschmidt); 1878, p 88 (Schweder).

2. The wet method is partially made use of when the percentage of copper is large. The processes are as follows:

a. The button consisting of Ni,As and Cu,As is dissolved in nitric acid, and evaporated to dryness with sulphuric acid. The residue is digested with aqueous sulphurous acid until no odor of the latter remains. The copper and arsenic (also antimony) are now precipitated from acid solution by sulphuretted hydrogen, and the arsenic sulphide (also antimony sulphide) is extracted with a warm solution of sodium sulphide. The residue remaining in the filter is washed and dried in the roasting dish in front of the muffle, and is then ignited. The copper sulphate is rubbed up and strongly heated, ammonium carbonate being added towards the end. The copper oxide which has been produced is weighed, and calculated to Cu,As. This is deducted from Ni2As+ Cu,As to determine the Ni,As (Patera).

b. By another method, the ore, etc., is dissolved, and the copper precipitated by the galvanic current (pp. 115 et seq.), and the remaining solution with potassium hydrate. The precipitate, containing iron, nickel, and cobalt, is washed, dried, ignited, arsenized, and the further process conducted as given in the dry method, p. 183. When much iron is present, it is better, on account of the labor of washing the iron precipitate, to prepare an assay according to Plattner, for Ni,As+Cu,As, to separate the copper from a second fresh charge by electrolysis, to calculate the copper to Cu,As, and deduct this from Ni,As+Cu,As, which will give the Ni,As (Schweder).

Nickeliferous pyrrhotine, with 0.82 per cent. Cu and 1.72 per cent. Ni and Co: 2 grammes (30.87 grains) are dissolved as above, p. H7, and the copper is precipitated by electrolysis from a solution of 40 cubic centimeters (2.44 cubic inches) of nitric acid, and 360 cubic