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oxygen of the acid are in equal quantity, and which consequently corresponds to the oxalic acid crystallized in water.
The decomposition of oxamide in oxalic acid and in ammonia, occasioned without doubt by the insolubility of the new salt, is far more prompt here than with the aqueous alkalies and acids.
The tribasic oxalate of lead is formed also by pouring oxalate of ammonia into a solution of tribasic acetate of lead; but in this case it presents itself under the form of an amorphous powder, and without lustre.
This salt, prepared in any manner, absorbs carbonic acid from the air, and finishes by becoming transformed into a mixture of neutral carbonate and oxalate of lead.
Acetic acid easily removes its excess of base.
The nitrate of lead is in the same case ; boiled with this salt, it changes it rapidly into neutral oxalate, whilst that in its turn becomes basic.
When, instead of causing the oxamide to re-act on the ammoniacal nitrate of lead, in presence of a large quantity of water, we operate on concentrated liquors, we see deposited, even during the ebullition, granulous crystals, which received on a filtre, washed with cold water and dried in vacuo, are formed of tribasic oxalate of lead, united to a neutral nitrate. The formula for this salt is
3 P60, C2 03 + 3 P60 Az205, H20. These same crystals maintained in the boiling liquor where they had birth, become changed gradually when this liquor contains neutral nitrate of lead, into another double salt, composed of oxalate and of nitrate of lead, which has for its formula
P60 C2 03, P60 Az2 OS, 2H20. It was presumed that these double salts, of which I have above spoken, were formed directly by the contact of neutral and tribasic oxalates of lead with the nitrate, under the condition of operating in liquors sufficiently concentrated. This is in fact what takes place.
The tribasic oxalate of lead, introduced into a boiling solution formed of one part of nitrate of lead and of two parts of water, changes into white crystals, bright and granulous, which are nothing more nor less than the first double salt formed by the combination of the tribasic oxalate, with the neutral nitrate of lead.
These same crystals are destroyed by a longer ebullition, and transformed into neutral oxalo-nitrate = Pb 0 C 03 + Pb 0 Az '0“, 2 H20.
The original water filtered boiling, leaves deposited on cooling, beautiful crystals, bibasic monohydrated nitrate of lead.
In all cases, the most simple means of preparing the latter of these double compounds, consists in making the two neutral salts which enter into the composition, act directly on each other.
The neutral oxalo-nitrate of lead crystallizes in very brilliant hexagonal laminæ, insoluble in cold water, slowly decomposed by it in nitrate of lead, which dissolves it, and in the neutral insoluble
oxalate. Boiling water destroys this salt with the greatest rapidity. When submitted to the action of heat, it loses its water, and leaves disengaged, very soon after, corroding vapours mixed with carbonic acid.
Bibasic Monohydrated Nitrate of Lead.—The bibasic nitrate of lead was known long ago, but only in the anhydrous state. M. Peligot has shown that it may be obtained combined with an atom of water.
This salt is but slightly soluble in cold water; much more soluble in boiling water, from whence it crystallizes with great facility in cooling. Carbonic acid decomposes it, and brings it back to its neutral state.
Dried in vacuo and raised to 100°, it does not loose the smallest quantity of water; it is only at a temperature much more elevated, and comprised between 1609 and 190°, that it loses its water of crystallization; and even then, this dehydratation takes place with extreme slowness. Towards 200° this salt becomes yellow, and sets at liberty a quantity of corroding vapours. At a red heat, it becomes destroyed completely, and furnishes 2e of its weight of oxyde of lead. It has given from analysis 3:1 of water, and 19 of nitric acid. It has for its formula then,
2 Pb O, Az? 03, HP 0. This salt is formed under many circumstances, but there are none of them more worthy of notice, than that I have just spoken of.
On slightly heating a mixture of white lead, nitrate of lead and water, the whole mass soon becomes agitated by a tumultuous movement. It sets at liberty carbonic acid with great abundance, and with such rapidity that one would almost believe that there is free nitric acid in the liquid. This, filtered boiling, leaves deposited on cooling, a considerable quantity of bibasic monohydrated nitrate of lead.
The basicity of salt of lead never descends beyond this limit, however great be the excess of white lead. I am assured of this by the examination of the salt, and by the nullity of action of bibasic nitrate of lead on the carbonate of lead.
Placed in the same circumstances as the nitrate of lead, the neutral acitate produces nothing similar ; it does not disengage the carbonic acid of the ceruse, and preserves itself intact.
The tribasic oxalate of lead, boiled with a large quantity of water, and with an excess of nitrate of lead, becomes changed into neutral oxalate, and in its turn the neuter nitrate becomes bibasic hydrated nitrate.
On the other side, when we boil a solution of the tribasic acetate of lead with an excess of the neutral oxalate, the filtered liquor is no longer troubled by the carbonic acid, a circumstance which shows that the former salt has ceded } of its base to the latter.
Sub ocide of Lead.-M. Dalony has announced that in decomposing the oxalate of lead by heat, we obtained a black amorphous powder,
which he considers as a new oxide less rich in oxygen than the protoxide or litharge. M. Boussingault repeated the experiments of M. Dalony, extended them and arrived at the same conclusions as he did. Most chemists, still leaning towards the opinion of our honourable colleague, have regarded the question as being not yet resolved. Some of them even, and particularly M. Winkelblek, deny the existence of a sub oxide of lead, and regard it, either as an atomic mixture of lead and its protoxide, or even as a variable mixture, though an intimate one, of these two bodies.
In again searching for the cause of this diversity of opinions, I have believed it possible to attribute it to the diversity of the products themselves, which ought to give oxalate of lead, by supposing that its decomposition by heat has been made at unequal temperatures. The results at which I have arrived confirm me in this idea.
Since then I have applied to the decomposition of the oxalate of lead the same rules which I made known in 1833, on the occasion of the pyrogenous products of tannin, and the result has been such as I expected.
The oxalate of lead, heated in a cucurbite placed in an oil bath, manifested signs of decomposition at a temperature bordering on 300.
The temperature was then maintained as stationary as possible.
The gases are disengaged with a great degree of slowness. They consisted of carbonic acid and oxide of carbon. They were collected and analysed throughout the whole duration of the operation, which was very long. They constantly presented the exact relation of 75 to 25, or 3 to 1. Toward the end only, when, in order to terminate the operation it became necessary to raise the temperature a little, the proportion of carbonic acid was a little augmented.
This relation of 3 to 1 between the carbonic acid and the oxide of carbon gases, is the same as that indicated by theory, by admitting that the fixed product of the cucurbit is a sub oxide, having for its formula Pb20, or a mixture of equal atoms of lead and oxide of lead.
In fact (P60 C203) = Pb20, or Pb + PbO + C40?, which becomes translated into C306 : 6 volumes of carbonic acid, and Co 2 volumes of oxide of carbon.
If we heat directly over charcoal, or the flame of a spirit lamp, the cucurbit which contains the oxalate, and which is the same as was done by M. Dalony, Boussingault, and Winkelblek, we have control no longer over the temperature, and the gases vary perpetually in their relations; a fact which indicates complicated decomposition.
The sub oxide of lead, prepared as I have said, and after having taken all the possible precautions to avoid it having contact with the air, is a compound perfectly definite. It is of a well grounded black, sometimes dull, sometimes rather soft like velvet. It does not contain metallic lead, and I prove it in a decisive manner, and at the same time very simply; by boiling it screened from contact
with the air, with a solution of cane sugar, which dissolves the litharge very well, and absolutely takes nothing from the sub oxide of lead.
The nitric, sulphuric, hydrochloric, and acetic acids, feeble or concentrated, do not form distinct salts with the sub oxide of lead; they change it into metallic lead, very finely divided, and into ordinary oxide, with which they combine.
The soluble alkalies act in the same manner. The nitrate of lead itself changes it into protoxide of lead and metallic lead. It disappears in a diluted solution of this salt, and the liquor filtered boiling, leaves deposited a mixture of nitrate and of basic nitrate of lead.
Mixed with a small quantity of water, in contact with the air, the sub oxide of lead acts in a remarkable manner, and of which we do not find any reasonable explication, except by admitting that it really constitutes a definite compound.
It then produces much heat, rapidly absorbs the atmospheric oxygen, and becomes converted into a white powder, which is the ordinary hydratic oxide. A mixture of lead, very finely divided, and litharge in a fine powder, produces nothing similar.
Heated to a dull red the sub oxide of lead becomes decomposed, and forms a mixture of lead and its protoxide. We recognise this decomposition with facility, whether by amalgamation, or with boiling sugar water, which dissolves the oxide, or with feeble acetic acid, which leaves a residue of lead, which in place of being in a fine powder, as with the sub oxide, presents itself in net work, which needs only to be compressed between the fingers to become a compact mass of a metallic aspect.
Besides, the mixture is immediately distinguished from the sub oxide by its colour, which is yellow, slightly tinged with green.
The tribasic oxalate of lead is decomposed by heat, like the neutral oxalate ; but the gases vary in their relations during the whole length of the operation, and the residue is a mixture of the sub oxide and of protoxide. I was assured of this upon using a boiling solution of sugar, which dissolved a considerable quantity of the protoxide of lead.
The analysis of the sub oxide of lead has not in any manner to be made after the examination of the relation of the gases proceeding from the oxalate.
This relation sufficiently indicates for the sub oxide the formula Pb20, which likewise confirms the properties of this compound.
100 parts of sub oxide heated in contact with the air, have given 103,7 and 103,6 of the protoxide.
This oxidation is effected with great facility, for the sub oxide of lead is pyrophoric, and when we heat it in a weight of its mass, the whole mass entire takes fire.
The incontestable existence, however, of the sub oxide of lead is important for the general history of the combinations of oxygen with the metals. This sub oxide will doubtless not remain long the only one of the species, but it will soon place itself at the head of a
series of compounds which will present, with the superior degrees of the oxidation of the metals, this very singular point of resemblance, that neither one nor the other can combine with the acids.
The oxalate of zinc gives from the dry distillation, the ordinary oxide of zinc, and sensibly too, equal volumes of carbonic acid gas and oxide of carbon.
That of copper is decomposed with the greatest facility; it sets at liberty carbonic acid almost pure, and gives a residue of copper quite metallic, in scarlet spangles, brilliant and malleable, some of which are several millimetres broad, although they certainly proceed from a pulverulent and amorphous matter, which has not been submitted
fusion. On the Theory of the Fabrication of Carbonate of Lead (ceruse). - The process for the fabrication of white lead, by M. Thenard, is well known, and was for the first time executed by M. Rouard, in his domestic economy of Clechy. This process, known under the name of the French process, to distinguish it from another kind of fabrication employed at first in Holland, consists in making carbonic acid pass into a solution of tribasic acetate of lead. This latter salt cedes to the carbonic acid the two of its base, which it deposits in the state of white lead, and thus becomes neuter. It may serve anew for the same operation, after its having combined directly with the oxide of lead. We conceive that a considerable quantity of ceruse may thus be produced, by a comparatively very feeble proportion of acetate of lead, and consequently by acetic acid. There would even be no limit to the production of ceruse with the same vinegar, if this salt did not retain a feeble quantity of acetate of lead.
A modification has been projected in England of the process of M. Thenard, by which they have, if I may so express it, transformed it into a process by the dry method. This process consists of mixing with litharge about the hundredth part of its weight of acetate of lead, and to cause to pass on the mixture, previously wetted with a very small quantity of water. In a few hours all the litharge is carbonated, and the operation is finished.
Carbonic acid and oxide of lead, alone, are only united with extreme slowness. It is necessary then to admit, that the some thousandth parts of acetic acid, which are found in the preceding mixture, are conveyed over the entire mass of oxide of lead, to constitute a basic ascetic, which is destroyed and re-produced without cessation.
That process named the Holland one, which was transported many years ago to Lille, where it has become a very important object of industry, consists in exposing the plates of lead to the vapour of vinegar and to the exhalation arising from horse dung. The vinegar made use of is that made from beer of an inferior quality, and which contains a very small quantity of real acetic acid. After an examination which I made of this vinegar, for which I am under considerable obligations to the courtesy of M. M. Lefevre and Decoster, manufacturers of ceruse at Lille, the weight of the real