residue is then moistened with a few drops of hydrochloric acid and diluted with 20 cubic centimeters (1.22 cubic inches) of water. To this are added 30 cubic centimeters (1.83 cubic inches) of ammonia and 15 cubic centimeters (0.91 cubic inch) of ammonium carbonate. The solu tion is allowed to settle and then filtered into a flask of 500 cubic centimeters (30.51 cubic inches) capacity. The filter is washed with 30 cubic centimeters (1.83 cubic inches) of warm ammonia, and finally with warm ammoniacal water. When much ferric hydrate is, present the precipitate is again dissolved and precipitated with ammonia and ammonium carbonate.-Plumbiferous ores: The assay sample is dissolved in nitric acid, and the solution evaporated with sulphuric acid. The lead and calcium sulphates are then filtered off. If the ore contains but little calcium, it may be treated with nitric acid, and the lead precipitated with 30 cubic centimeters (1.83 cubic inches) of ammonia, and 15 cubic centimeters (0.91 cubic inch) of sodium phosphate. When much calcium is present, the precipitate is again dissolved and precipitated.

A stand with three shelves is used. The uppermost shelf serves for the reception of the flask containing the sodium sulphide, the second smaller one, for a small flask with a pipette containing the indicator solution, and upon the lowest shelf, which projects somewhat, the flask containing the solution of zinc is placed. Over this, hangs a burette with a pinch-cock fastened to arms on the vertical wall, its mouth being directly under the orifice of the pinch-cock on the flask containing the standard solution. Duplicate titrations are then made, between which only decimal differences are allowable. Suppose E is the weight of the assay sample in cg., Q the quantity of standard solution in c. cm. used for the precipitation, M

the total quantity of the assay solution in c. cm.; the titer will be

100 E
[2-(M× 0.007)]

if hydrated peroxide of iron has been used as the indicator, or

if paper saturated with ferric chloride (p. 209) has been used.

In titrating the samples, one-third to one-half of the approximate quantity of the precipitating agent required should be added every time to the solution and this well shaken. A drop of solution of ferric chloride is added to the zinc solution from a small pipette. The mass of hydrated peroxide of iron which is formed is broken up into as equally sized flakes of 1 to 1.5 millimeters diameter (0.039 to 0.059 inch) as possible by vigorously swinging the flask to and fro. This swinging is constantly continued while solution of sodium sulphide is added by cubic centimeters, until the color of the flakes. commences to change. A minute is then allowed for the reaction of the particles of liquid which have remained ineffective, and the precipitation is then finished by adding sodium sulphide drop by drop. If Vis the quantity of the precipitating agent consumed in c.cm., T the titer, M the total quantity of the solution in c.cm. after the assay is finished, the percentage of zinc when ferric hydrate has been used as indicator, will be—

when slips of paper saturated with ferric chloride have been used. When the first plan is employed the titration must be continued, in order to ascertain the titer, until the flakes become entirely black, but, in titrating solutions of ore, only until the reddish-brown color has passed into a greenish tint. The following conditions are required for obtaining a sharp reaction: the flakes must be nearly of the same size, the flask should be carefully swung to and fro to prevent the flakes from being broken up any further; not too much of the precipitating agent must be added at one time, and it should not fall directly upon the flakes, but run down the sides of the flask; the titration should be done at the ordinary temperature, whereby the reaction appears more gradually and uniformly, but the precaution must at the same time be observed of adding the standard solution at longer intervals; uniformity of quantity and time in treating the assays; judging the tone of color by reflected light; and finally the flake reaction should be controlled by a drop test.

If it is required to determine the amount of over 0.5 per cent. of lead in zinc ore, 2 grammes (30.87 grains of the sample are dissolved in nitric acid and evaporated to dryness. Some diluted sulphuric acid is added to the dry mass, and this is again evaporated until white vapors appear. It is allowed to become cold, diluted with 20 cubic centimeters (1.22 cubic inches) of water, filtered, and washed until the wash water shows no reaction with ammonium sulphide. The precipitate (lead sulphate, calcium sulphate, gangue) is rinsed off into a beaker and digested with a mixture of ammonium tartrate and ammonia in excess. The lead solution is filtered off, the lead precipitated with sulphuric acid, and the lead sulphate dried and weighed; or, it is detached from the filter, the latter incinerated, and the precipitate ignited (see also p. 98).

Arsenical iron in nickel ores, slagging | Bischof on colorimetric process for lead,

Belgium, treatment of lead matt in, Bromyrite, 131
89

Berlin School of Mines, furnaces used Bullion or button balance, 70
in, 54
Berthier on the reducing power of Bunsen's method for manganese, 252