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intensity produced by the union of non-gaseous oxygen with zinc is to the intensity necessary to separate water into non-gaseous oxygen and gaseous hydrogen, as 1:93:1; aud 1.32:1:: 1:93 + 1.9: 1+1.9. Wherefore, the intensity necessary to give oxygen the gaseous form is to the intensity necessary to separate water into pongaseous oxygen and gaseous hydrogen as 1.91: 1.

45. Thus we see that a very great intensity of current is employed in changing the condition of bodies, as well as in separating them from their combinations. The field of investigation here opened is very extensive, but I may not at present enter further upon it. I will only remark, that if the intensity necessary to convert a body into a different state, compared with the heat or cold due to the mechanical or other production of that different state, be such as accords with the relations of intensity and heat which we observe in the voltaic apparatus, we have a proof that some of the effects which are usually referred to “latent beat,” are in fact nothing more than the recondite operations of resistance to electric current.*

46. In our investigation into the cause of the heat of combustion, it will be necessary to deduce our calculations from the electric intensity which is required in order to reduce the product of combustion to the state in which its elements were prior to combustion. The following is a list of these intensities, reckoning the decomposition of water into its gaseous elements as unity,

47. Intensity necessary to decompose oxide of zinc into gaseous oxygen and metal, from (42) and (44), is 3.7 pairs of Smee's battery, or 1.32 h.

48. Intensity necessary to decompose protoxide of iron into gaseous oxygen and metal.- From (43), 3:3 of Smee's pairs =i: and from (41), 2.8 pairs h; whence 2.8 i = 3:3 h, or i = 1:18.

49. Intensity necessary to decompose potassa into potassium and gaseous oxygen.– From (144) and (37) we have 1.93 + 1.9 : 4:06 + 1.9 :: 1.32 h : 2.05 h the intensity required; which may be otherwise expressed by 5-74 of Smee's pairs. Heat evolved by Combustion, when it terminates in the formation

of an Electrolyte. 50. Finding that our information on the quantity of heat evolved by the combustion of metals was not very satisfactory, I have without wishing to depreciate the labours of Duloug, Despretz and others, thought it right to bring forward such of my own experiments as are necessary in order to make my investigation complete.

51. I provided two glass jars. The smaller had an internal capacity of 90 cubic inches; and when placed within the other jar, as represented by Fig. 7, the space left between the two was sufficient to contain three pounds of water. By means of a scale, s, suspended by wire from a thick fold of moistened paper, I was able to introduce a combustible within an atmosphere of oxygen, and by means

Some experiments, which I have not time to refer to at present, render this hypothesis more than probable.

of a heavy weight I could keep the paper, sufficiently close to the top of the jar to prevent the escape of any considerable quantity of heated air, while at the same time it was not so tight as to prevent the admission of air as the oxygen was consumed. The increase of the temperature of the water was measured by a thermometer of great sensibility.

52. The heat evolved by the combustion of zinc was ascertained in the following manner.

The smaller jar was filled with oxygen, placed in the other jar, and surrounded by three pounds of water, the heat of which was contrived to be as much below the temperature of the surrounding air as it was expected to exceed it at the close of the experiment. A piece of phosphorus, weighing ():4 grain, was then put into the scale, and over it I placed a heap of fine zinc turnings, weighing 50 grains. I now ignited the phosphorus, and plunged the scale into the inner jar. After the combustion had terminated, and the heat thereby evolved had been evenly distributed throughout the water by stirring, the increase of temperature was poted. The contents of the scale were then thrown into dilute sulphuric acid, and the volume of hydrogen thereby evolved indicated the quantity (generally about 15 grains) which had not been burnt. Two-tenths of a degree of heat were deducted from the observed heat, on account of the phosphorus, and an allowance having been made, on account of the capacity of glass for heat, the results were reduced to the standard of one pound of water.

53. The mean of several experiments conducted in the above manner, showed that the heat evolved by the combustion of 32:3 grains of zinc is able to increase the temperature of a pound of water by 10°.8.

54. The heat evolved by the combustion of iron was ascertained in a similar way. The iron was in the state of fine wire, and that portion of it that was not burnt was carefully collected, weighed, and deducted from the original quantity. The mean of several trials indicated that 28 grains could increase the temperature of a pound of water by 9°:48.

55. Heat evolved by the combustion of potassium.-This metal, in pretty large lumps, was introduced into an atmosphere composed of equal bulks of oxygen and air. I then introduced a stout iron wire, sharpened at the end, into the jar, and with it I cut the potassium into small pieces. Under this treatment it soon became so soft, that

every

time the rod was lifted it wonld draw out a string of metal. In this state it often ignited, and the experiment was spoiled on account of the partial formation of peroxide. However, by careful management, I succeeded in making some good experiments, in which nearly all the potassium was converted into potassa ; and the exact quantity of unoxidized metal was ascertained by observing the volume of hydrogen evolved when the contents of the scale were exposed to the action of water. The mean of these showed that the heat evolved by the conversion of 40 grains of potassium into potassa is able to increase the temperature of a pound of water by 17°:6.

56. Heat evolved by the combustion of hydrogen.-- The gas was burned in an atmosphere of oxygen, diluted with common air, by means of a jet furnished with a very narrow bore. A grain of hydrogen evolved as much heat as is able to increase the temperature of a pound of water by 8°:36.

57. We shall now proceed to examine how far the theory of resistance to electric conduction agrees with the above experimental results.

58. We have seen (47), (48), and (49), that the intensities of the affinities which unite gaseous oxygen with zinc, iron, potassium and gaseous hydrogen, are as 1:32, 1:18, 2:05 and 1; and the proportional quantities of heat which were generated by the combustion of the equivalents of these bodies, are 10°:8, 9°:48, 17°:6, and 8°:36, or 1:29, 1:13, 2:105 and I, a ratio which is very nearly the same as that of the intensities just given. Hence we see that the quantities of heat which are evolved by the combustion of the equivalents of bodies are proportional to the intensities of their affinities for oxygen. Now I proved in my former paper* that a similar law obtains in the voltaic apparatus, in consequence of its heat being produced by resistance to conduction. And hence we have an argument that the heat of combustion has the same origin.

59. But our proof of the real character of the heat of combustion is rendered more complete by regarding quantities as well as ratios of beat. From the quantity of heat generated by the motion of a given current along a wire of known resistance, we can deduce the quantities of heat which, according to the theory of resistance to electric conduction, ought to be produced by the combustion of bodies; and then these theoretical deductions may

be

compareil with the results of experiment.

60. The mean of three careful experiments detailed in my former papert, shows that if a wire, the resistance of which is an unit, be traversed by an electric current of 1°88 QI for one hour, the heat evolved by that wire will be able to increase the temperature of a pound of water by 15°:12. Now I have ascertained experimentally, that a pair consisting of amalgamated zinc and platinized silver, excited by dilute sulphuric acid, is able to propel a current of 0°.168 Q against the whole resistance of the circuit, when that resistance is 5-2; consequently, a similar pair can propel a current of 0°.168 Q x 5.2 00:874 Q against the resistance which I have called an unit. But from (42) the intensity necessary to separate oxide of zinc into zinc and gaseous oxygen, is to the intensity of one of Smee's pairs as 3:7:1; consequently, the electricity produced by the union of zinc and gaseous oxygen must be sufficiently intense

Philosophical Magazine, October 1841, S. 3, vol. xix, p. 275. (70.)

Ibid. p. 266. | I beg to remind the reader that my degree, expressed thus (1°), indicates that quantity of current electricity which, after passing constantly during one hour, is found to have electrolized a chemical equivalent expressed in grains; as, 9 grains of water, 36 grains of protoxide of iron, &c.

2

to propel a current of 09.874 Q x 3.7 = 30.234 Q against an unit of resistance. Now, 1o.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 150.12; therefore 3o.234 Q could, in the

3.234 same circumstances, produce 1-88

x 150.12 = 440.74 of heat. But in (70) of my former paper, 1 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 44074; 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 13°.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, 17o.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 (61) 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 90.6. 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,

October 5, 1841.

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, C? 0, and on the other part, amidogene, Aza, H4.

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 HAz* 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 PbO, C°,03, in which the oxygen of the base and the

Comptes Rendus, December 6th, 1841.

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