same circumstances, produce (1234); 1.88 to propel a current of 09-874 Q × 3·7 = 3°·234 Q against an unit of resistance. Now, 10.88 Q, when urged against an unit of resistance, was able in one hour of time to increase the temperature of a pound of water by 15.12; therefore 3°.234 Q could, in the × 15o•12 = 449.74 of heat. But in (70) of my former paper, I proved that the same quantity of heat should always (according to the theory which refers the whole of the heating power of the voltaic apparatus to resistance to the electric current) be produced by a given quantity and intensity of electrolysis, whether the resistance opposed to the current be small or great. Wherefore the heat, which on these principles ought to be generated by the combustion of 3.234 equivalents of zinc, is 449.74; or, in other words, one equivalent, or 32-3 grains of zinc, should generate heat sufficient to increase the temperature of a pound of water by 139.83. 61. Now, as I have before stated, the quantities of heat evolved by the combustion of the equivalents of bodies, ought, according to the theory of resistance to electric conduction, to be proportional to the intensities of their affinities for gaseous oxygen. These, in the cases of zinc, iron, potassium, and hydrogen, are 1.32, 1∙18, 2.05 and 1. Hence 13°-83, 12°-36, 21°-47, 10°47 are the quantities of heat which ought, according to our theory, to be produced by the combustion of 32-3 grains of zinc, 28 grains of iron, 40 grains of potassium, and 1 grain of hydrogen. 62. By comparing these results of theory with the quantities of heat, 10°.8, 9°48, 17° 6, and 8°.36,* which were (53–56) obtained from experiment, it will be seen that the former exceed the latter by about one quarter. Considering the difficulty of preventing some loss of heat, in consequence of the escape of air from the mouth of the inner jar (51) during the first moments of combustion, &c., it will, I think, be admitted that experiment agrees with the theory as well as could have been expected. 63. I conceive, therefore, that I have proved in a satisfactory manner that the heat of combustion (at least when it terminates in the formation of an electrolyte) is occasioned by resistance to the electricity which passes between oxygen and the combustible at the moment of their union. The amount of this resistance, as well as the manner of its opposition, is immaterial both in theory and in experiment; and if the resistance to conduction be great, as it most probably is when potassium is slowly converted into potassa by the action of a mixture of oxygen and common air: or little, as it probably is when a mixture of oxygen and hydrogen is exploded; still the quantity of heat evolved remains proportional to the number of equivalents which have been consumed, and the intensity of their affinity for gaseous oxygen. Crawford, whose method was well adapted to prevent loss of heat, obtained 99.6. More recently, Dalton observed about 89.5. 64. That the heat evolved by other chemical actions, besides that which is called combustion, is caused by resistance to electric conduction, I have no doubt. I cannot, however, enter in the present paper upon the experimental proof of the fact. Broom Hill, Pendlebury, near Manchester, Memoir to serve as a History of the Combinations of Lead. By M. J. PELOUZE.* Oxamide and allantoine, in acting on the elements of water, by the intermediation of the alkalies, transform each other into oxalic acid and ammonia. According to M. Dumas, the first of these substances, for the discovery of which we are indebted to him, is formed of two radical compounds, which are, one part the oxide of carbon, C2 O2, and on the other part, amidogene, Az, H. M.M. Liebeg and Wöhler, who have made us acquainted with the artificial production of allantoine, have not indicated what appeared to them to be its most probable formula, but it is clear that the composition C4 H6 Az4 03, does not permit the supposition that it contains the oxide of carbon and of amidogene, which pre-existed there as in oxamide. This observation agreeing but indifferently with the ideas generally adopted by chemists on the constitution of amides, and in particular that of oxamide, I have undertaken, on this latter substance, some experiments directed principally with the aim of uniting it with the metallic oxides, by causing it to lose its water, as M. M. Liebeg and Wöhler have succeeded in accomplishing with allantoine. If, in effect, oxamide has suffered a loss of water in its union with the bases, this dehydratation would be sufficient to shew that it contains neither oxide of carbon nor amidogene, since we know that in a state of liberty the oxamide is left represented without residue by these two binary compounds. I endeavoured then to unite the oxamide to the oxide of silver, and to the oxide of lead, but I could not procure this result. Under this relation the question of amides does not receive any new light, but in pursuing these enquiries I arrived at some novel results, which will form the principal object of my memoir. A boiling solution of oxamide is not altered by the nitrate nor by the acetate of lead; but if we add to either one or the other of these salts a little ammonia, we shall soon see precipitated in abundance small white plates or laminæ, brilliant, and soft to the touch, which are formed of 90'5 of the oxide of lead, and 9.5 of anhydrous oxalic acid. It is a new degree of saturation of the oxalic acid, an oxalate of lead tribasic, = 3 Pb0, C2, 03, in which the oxygen of the base and the 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 Pbo, C2 03 + 3 Pb0 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 Pbo C2 03, Pb0 Az2 05, 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 C303 + Pb 0 Az 203, 2 H2 0. 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 160° 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 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 0, Az2 0,, H2 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 oxide 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 (Pb0 C203) = Pb20, or Pb + Pb0 + C107, which becomes translated into C30° 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 |