which could not be detached from it. In this case, it is necessary to add 0.5 to 0.6 gramme (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 Co2As 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 copper1 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 (Ni2As+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

1 B. u. h. Ztg. 1868, p. 24; 1868, p. 94 (Kleinschmidt); 1878, p S8 (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. 117, and the copper is precipitated by electrolysis from a solution of 40 cubic centimeters (2.44 cubic inches) of nitric acid, and 360 cubic

centimeters (21.96 cubic inches) of water (p. 115); or 5 grammes (77.16 grains) of ore are roasted and charged with arsenic in a soda paper cylinder (p. 185), and fused with fluxing agents in the crucible (p. 186); the iron is slagged off twice and the button then dearsenized. If cobalt is absent, Ni,As+ Cu, As will remain behind, and the nickel is then calculated as previously stated (p. 187). Cobalt and nickel may also be determined by electrolysis, and caculated to (Ni,Co), As, and the Cu, As determined from the difference.

c. Compounds difficultly soluble, as, for instance, slags. -These are roasted, arsenized, and fused according to the process given on p. 183. If they are poor in nickel, several buttons (say five) are wrapped in a cornet and treated with borax, as before described. The iron is slagged off, the excess of arsenic removed, and the button (Ni2As+Cu,As) weighed. It is then dissolved in 20 cubic centimeters (1.22 cubic inches) of nitric acid, 200 cubic centimeters (12.2 cubic inches) of water are added, and the copper is precipitated by electrolysis until it commences to be colored black by the arsenic (p. 118). The Cu,As is calculated from the precipitated copper, and deducted from the Ni,As+ Cu,As, etc., or, what is still better, in order to avoid constantly watching the precipitation of copper, lest arsenic be precipitated with it, the button of Ni2As+Cu,As is dissolved in nitric acid, in a covered beaker-glass, then evaporated to dryness, and the copper and arsenic are precipitated with sulphuretted hydrogen. The filtrate is heated in order to drive off the sulphuretted hydrogen, ammonium sulphate and ammonia are added, and the nickel determined by electrolysis (see later on). This is calculated to Ni,As, which is deducted from NiAs+ Cu, As, and Cu,As is found from the difference.

C. Compounds containing antimony.

If a large amount of antimony is present, it becomes necessary to remove it from the dissolved ore by sulphur