Lead acetate

“ Neutral lead acetate comes into commerce in the form of colourless heavy crystals, which are often covered by a white powder of the basic acetate; they dissolve readily in water, and the solution has a sweetish taste, hence the name “sugar of lead”. Frequently the solution is very turbid; this is caused by the carbonates contained in the water. The turbidity may be removed by the addition of a little acetic acid. It is only economical for the colour maker to prepare sugar of lead when he can obtain cheap raw materials, lead or litharge and vinegar. ”

“ After about 12 hours, by the simultaneous action of the vapours of acetic acid and the oxygen of the air, lead acetate is formed. Carbonic acid is now led into the chambers. The carbonic acid is obtained by burning charcoal in a cylindrical furnace; it is cooled by being passed through a long iron tube before it enters the chamber. For 12,500 kilogrammes of lead there are required every day about 482 litres of dilute acetic acid, obtained by mixing strong acetic acid with water until the mixture contains 4·5 per cent. ”

“ White lead is prepared according to very different methods, the principle of which consists in subjecting a solution of tribasic lead acetate to the action of carbonic acid, by which the basic carbonate is produced and the neutral acetate formed, the latter being then reconverted into the basic acetate, which again serves to produce white lead and so on. ”

“ The formation of lead oxide is especially marked from the fact that with a sufficient quantity of air [137] not only is the normal lead acetate formed but also the basic salts. [47]
When oxidising in the presence of air, [48] when heated or in the presence of an acid at the ordinary temperature, lead forms compounds of the type PbX2. Lead oxide, PbO, known in industry as litharge, silberglätte (this name is due to the fact that silver is extracted from the lead ores of this kind) and massicot. ”

“ Almost insoluble in water; insoluble in alcohol. Lead oxide is only valuable for its preparations.
PREPARATIONS PLUMBI ACETAS—LEAD ACETATE—SUGAR OF LEAD
Derivation.—Heat lead oxide in acetic acid and water. Lead acetate crystallizes on cooling.
Properties.—Colorless, shining, transparent; monoclinic prisms or plates, or heavy, white crystalline masses, or granular crystals, having a faintly acetous odor and a sweetish, astringent, afterwards metallic taste. Efflorescent and absorbing carbon dioxide on exposure to the air. Soluble in two parts of water and in thirty parts of alcohol. ”

“ Pure acetate of lead forms colourless, transparent, prismatic crystals, slightly efflorescent in dry air; it is soluble in 8 parts of alcohol and in 11⁄4 part of cold water; the aqueous solution has a sweet astringent taste, and feebly reddens litmus, but turns turmeric and the juice of violets green; when gently heated, it melts in its water of crystallisation; by continuing the heat, the whole of the water is expelled, and the dry acetate obtained; at a higher temperature the salt suffers decomposition, and acetic acid, acetone, &c., is given off. ”

“ The solution of acetate of ammonia may be recovered from [232] the white lead, and be repeatedly used, for the conversion of further quantities of oxide of lead into hydrate and acetate of lead, which hydrate and acetate are converted into carbonate of lead by the injection of carbonic acid. Theoretically, a given weight of acetate of ammonia in solution, used in conjunction with carbonic acid, should be capable of converting an unlimited quantity of oxide of lead into carbonate of lead ”

“ The colouring matter is not yet quite pure; the treatment with lead acetate and sulphuretted hydrogen must be repeated, the solution then obtained is evaporated at a low temperature, the residue dissolved in boiling alcohol, phosphoric acid added to decompose traces of lead carminate still present, then ether, finally the clear liquid is separated from the precipitate and evaporated. ”

“ Neither the strong acids nor alcohol, when considerably diluted, occasion any disturbance in it; but sulphuric æther and its compound spirit, the tincture of muriated iron, and sub-acetate of lead, produce very dense precipitates: the acetate of lead only occasions decomposition, when an alkaline salt is present in the formula; the volatile alkali curdles the mucilage, and hard calcareous waters render the mixture difficult and often impracticable. ”

“ It is a monobasic acid, forming one normal and two acid potassium salts, and basic salts with iron, aluminium, lead and copper. Ferrous and ferric acetates are used as mordants; normal lead acetate is known in commerce as sugar of lead (q.v.) ; basic copper acetates are known as verdigris (q.v.) .
Pharmacology and Therapeutics.—-Glacial acetic acid is occasionally used as a caustic for corns. The dilute acid, or vinegar, may be used to bathe the skin in fever, acting as a pleasant refrigerant. Acetic acid has no valuable properties for internal administration. ”

“ Soft White Lead.—The hard white lead prepared as just described consists of very heavy and very hard lumps of the purest white. When soft white lead is required, the admixed lead acetate must be removed by washing. This is accomplished by adding a larger quantity of water, either when grinding under the edge-runners or in the mills, so that a thin pulp is formed; this is run into a receiver, in which is a stirrer. The white lead is not completely prevented from sinking by the stirrer ”

“ After cooling thoroughly, the cold basic acetate, which may now have crystallised or separated out more or less, according to the strength of the solution, is treated with carbonic acid gas, whereby the basic acetate, in the presence of the ammonia set free, is converted into basic carbonate of lead of exceptionally white colour, and with high basicity and covering power, proper care being taken as specially indicated later on. ”

“ A crystalline substance, possessing a sweet taste, and blackening when exposed to SH2, can, under the circumstances, be no other substance than acetate of lead.
If the analyst does not care for this method, there is room for choice. Lead in solution can be converted into sulphide; in this case it is, however, absolutely necessary that there should be no great excess of acid, since as little as 2·5 per cent. of free hydrochloric acid will prevent all the lead going down. ”

“ When we attempt to ascertain the relative preserving power of the neutral salts, it will appear that those whose acid forms with the lead a soluble salt of lead are the least energetic; while those whose acid forms an insoluble salt of lead are most energetic. The protecting powers of acetate of soda, nitrate of potass, muriate of soda, sulphate of lime, arseniate of soda, and phosphate of soda, are inversely as the solubility of the acetate, nitrate, muriate, sulphate, arseniate, and phosphate of lead. ”

“ A subacetate of lead is formed by digesting a cold solution of uncrystallized acetate, over litharge, with frequent agitation. It is said that 65 pounds of purified pyrolignous acid, of specific gravity 1·056, require, for making a neutral acetate, 58 pounds of litharge ”

“ It is the RADICAL VINEGAR of the alchemists, and it is that which is preferred by the perfumers. Well-dried acetate of lead, or of iron, as well as several other acetates, may be substituted for acetate of copper in the above process; but are less economical and convenient. In all cases, great care must be taken to avoid over-firing, as thereby the quantity obtained is lessened, and the quality injured. The residuum of the distillation is pyrophoric and frequently inflames spontaneously, on exposure to the air. ”

“ Nitrate of lead offers no advantages over the acetate, and is generally more expensive to use. Free nitric acid is more objectionable than free acetic acid, because it may act as a solvent on chrome yellow and liberate free chromic acid, which is liable to “turn” the yellow. When using lead nitrate it is preferable to neutralise potassium bichromate with soda, to avoid the presence of free nitric acid. ”

“ Acetate of lead is now added to the filtrate until no further precipitation occurs; the liquid is then boiled and filtered. The meconic acid remains on the filter as meconate of lead, while the filtrate contains the morphine as acetate. The liquid is freed from excess of lead by passing through it a current of sulphuretted hydrogen, filtered to remove the precipitated sulphide of lead, and the [Pg 340] resulting liquid evaporated to an extract on a water bath, and treated with alcohol. The alcoholic solution on evaporation gives acetate of morphine, which may then be tested. ”

“ Acetate of lead is soluble in water and in alcohol. The subacetate is a more active poison than the neutral acetate. Sugar of lead is popularly considered as an active poison, but this does not appear to be the case. Sir R. Christison gave eighteen grains daily in divided doses for eight or ten days with no other unpleasant symptoms than slight colicky pains in the abdomen. Lead is probably eliminated from the system by the urine, and also by the milk; but there is reason to believe that when once deposited in the body, some considerable time is required for its complete elimination. ”

“ The alkaline liquor must be supersaturated with muriatic acid, and evaporated to dryness. The liquor acidulated, and deprived of its silica by filtration, is to be supersaturated with ammonia; when the alumina will precipitate in the state of a subphosphate. When the liquor is now supersaturated with acetic acid, and then treated with acetate of lead, a precipitate of phosphate of lead almost always falls. There is hardly a bit of iron to be found which does not contain phosphorus. The slightest trace of chrome is detected by the yellow colour of the lead precipitate ”

“ If, however, organic matters are specially searched for lead, hydrochloric acid is not the best solvent, but nitric should always be preferred; and, if there is reason to think that the lead exists in the form of sulphate, then the proper solvent is either the acetate or the tartrate of ammonia; but, in either case, the solution should contain an excess of ammonia. It must, however, be remembered that organic matters retain lead with great tenacity, and that in all cases where it can with any convenience be effected, the substances should be not only carbonised, but burnt to an ash ”

“ To protect the workman against poisoning by this lead compound, precautions must be taken against breathing in the dust. The simplest and most efficacious is to tie a wet sponge over mouth and nose; this retains the particles of dust in the inspired air. The dust, scraped off the cakes, is put into water, in which the salts dissolve, whilst the chrome yellow sinks to the bottom. In this process for preparing chrome yellow the solution of potassium acetate left after the precipitation contains a considerable quantity of free acetic acid, which may be utilised to dissolve lead. ”

“ Acids; fixed alkalies; alum; lime water; sulphate of magnesia; corrosive sublimate; nitrate of silver; and the sulphates of zinc, copper, and iron. Acetate of lead produces also a copious precipitation, but this depends upon the presence of the carbonic acid diffused through the solution, which decomposes the salt and forms an insoluble carbonate of lead. Magnesia likewise, contrary to what might be supposed, decomposes the solution and renders it pungent, from the extrication of ammoniacal gas ”

“ White lead, as obtained by precipitation from the acetate, subacetate, and subnitrate, is a true carbonate of the metal, consisting of one prime equivalent of lead 104, one of oxygen 8, and one of carbonic acid 22 ”

“ During this period the temperature rises to 75° to 80° C., considerable evolution of carbonic acid gas takes place, and the lead is converted first into acetate and subsequently the white basic carbonate. The layers (white beds) are uncovered and the corroded strips (corrosions) collected by hand. They are placed in trays and carried to heavy steel rollers by means of which and subsequent raking in wash becks the carbonate is detached from the uncorroded central core of blue lead. In many factories corrosions are now conveyed from the stacks to the wash becks or rollers by travelling cranes. ”

“ Further evidence given by the inoculation experiments shows the relationship between the more soluble and the insoluble lead salts. The dose of acetate required to kill an animal was about 0·1 gramme of acetate per kilogramme body weight. On the other hand, 0·1 gramme of white lead produced no ill-effects, 0·5 gramme per kilogramme body weight produced death in about two months. In addition, those animals suffering from the more acute forms of poisoning developed definite eye changes and retinal hæmorrhages. ”

“ All the precipitates of lead salts, with the exception of the sulphide, are soluble in fixed alkalies, in ammonium acetate, ammonium tartrate, and ammonium citrate. It is possible to determine the presence of lead in a large volume without evaporating down the whole bulk of fluid. By this means liquid containing lead is treated with sulphide of copper, sulphide of mercury, or baryta-water. Meillère states that he has detected the presence of as small a quantity as 1 milligramme of lead in 1,000 c.c. ”

“ 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. ”