One half of the lead thus obtained is put into a dry cupel of bone ash, and placed in the cupelling furnace, and treated as described in the article on assaying; the metallic button left on the cupel is then detached and weighed. The weight, divided by 5, gives the per-centage of pure silver.
Obs. The flux commonly employed in the above assay is composed of red argol, 6 parts; nitre, 4 parts; borax, 2 parts; fluor spar, 1 part; well pulverised and thoroughly mixed together. When the ore is very refractory, about a spoonful of carbonate of potassium should be added for each 1000 grains of ore, in which case the roasting may be dispensed with. The quantity of silver in argentiferous galena varies from 3⁄10000 to 1⁄3 part of the whole. Whenever this ore contains above 2 parts of silver in the 1000, it is found to be profitable to extract the latter. Indeed, by Pattison’s process it is found that as small a proportion as 1 in 8000 can be extracted with profit.
Uses. The uses of lead in the arts are well known. It enters into the composition of many important alloys (pewter, type-metal, shot-metal, solder, &c.), it furnishes us with several valuable pigments (chrome yellow, &c.), and it is extensively used in dyeing. Some of its preparations are employed in medicine.
Ant., &c. Administer an emetic of sulphate of zinc or sulphate of copper, and, if necessary, tickle the fauces with the finger or a feather, to induce vomiting. Should this not succeed the stomach-pump may be had recourse to. Epsom or Glauber’s salts, or alum, dissolved in water, or water acidulated with sulphuric acid, followed by tea, water gruel, or barley water, are the proper antidotes, and should be taken as soon after the poison has been swallowed as
possible. In poisoning by white lead, Dr Alfred Taylor recommends the administration of a mixture of sulphate of magnesium and vinegar, as preferable to the sulphate alone. When the symptoms are those of painter’s colic, the treatment recommended under that head should be adopted. In paralysis arising from lead, small doses of strychnine and its preparations may be cautiously administered. A symptom of poisoning by lead is the formation of a narrow leaden blue line, from 1⁄20th to 1⁄6th of an inch wide, bordering the edges of the gums, attached to the neck of two or more teeth of either jaw. (Dr Burton.) This discoloration may often be detected or rendered more conspicuous by rinsing the mouth out with water holding a little sulphuretted hydrogen or sulphydrate of ammonium in solution. Chevallier and Rayer recommend the use of sulphurous or hepatic mineral waters, or of artificial solutions of sulphuretted hydrogen or alkaline sulphides in water, both in cases of acute and chronic poisoning by lead; but the practical success of this plan does not appear to have been in proportion to theoretical anticipations. The moist and freshly precipitated sulphides of iron are said by their advocates to be infallible if taken sufficiently early.
Lead in Aerated Water. Some time since Sir Robert Christison condemned the use of syphons for lemonade, owing to the action of free tartaric acid upon lead, and the rapidity with which waters containing any free acid become charged with lead in syphons. According to Professor Miller, 0·0175 gr. of lead per gallon is not an unusual amount for average cistern water. Mr John S. Thompson, however, reports to the Edinburgh University Chemical Society that, after such water has been aerated and put into a syphon, the amount of lead dissolved in it begins to rise in a rapid manner. Thus in potash water, drawn from a syphon, 0·0408 grain of lead per gallon was found to be present, being nearly 25 times the quantity found in the same water before it entered the syphon. Pure aerated water again drawn in a similar manner from a syphon gave 0·0816 gr. of lead per gallon, or exactly double the amount found in the potash water, showing at once the well-known protective action that salts of the alkalies and alkaline earths have on lead. “Although,” says the ‘Medical Journal,’ “these results are sufficiently high and alarming; still, when the water is drawn off in small quantities at a time, as is frequently the case with invalids, the results are found to be still higher; thus, when potash water was so treated, 0·0455 gr. of lead per gallon was found, while aerated water, drawn off in small quantities, gave 0·0933 gr. of lead per gallon, showing a very marked rise in both cases. The cause of this increase in quantity of the lead appears to be owing, not so much to the lengthened period of contact between the liquid and the metal as to the fact that the nozzle of the
syphon, being exposed to the atmosphere in a moist state, becomes rapidly oxidised or carbonated, and is left in the most suitable condition for entering into solution, so that, when merely small portions of the liquid are drawn off each time, a comparatively concentrated solution of lead is obtained. These results,” continues the same authority, “compare accurately with those which were obtained by Messrs Savory and Moore, in examining the contents of a series of syphons of aerated water for Dr George Owen Rees, F.R.S., whose attention was drawn to the subject by detecting symptoms of lead-poisoning in himself after he had been in the habit for some time of drinking such aerated water.”
Lead, Acetate of. Pb(C2H3O2)2. Syn. Plumbic acetate, SUGAR OF LEAD, PLUMBI ACETAS. (B. P.) Prep. Litharge (in fine powder) 24; acetic acid, 40; distilled water, 20; mix the acetic acid and the water, add the litharge, and dissolve with the aid of a gentle heat, filter, evaporate until a pellicle forms, and crystallise. Drain and dry the crystal.
Acetic acid (sp. gr. 1·0843), 23 parts, is gently heated in a copper boiler rendered electro-negative by means of a large flat piece of lead soldered within it, and litharge (pure, and in fine powder), 13 parts, is sprinkled in; the heat is then continued, with constant stirring, until the acid is saturated, when the mother-waters of a former process, if any, are added, and the whole is heated to the boiling point, and allowed to settle until cold; the clear portion is now decanted, and evaporated in a similar vessel until the liquor has the sp. gr. 1·266 or 1·267, when it is run into salt-glazed stone-ware vessels (the edges of which have been well smeared with candle grease), and allowed to crystallise. The product is 38 to 381⁄2 parts of crystallised sugar of lead. It is found to be advantageous to preserve a very slight excess of acid during the boiling and crystallisation, to prevent the formation of any basic acetate the presence of which impedes the formation of regular crystals.
From litharge, 112 lbs.; acetic acid (sp. gr. 1·057), 128 lbs. Prop. 180 to 184 lbs.