150 



CHEMISTRY. 



of instances, however, illustrations occur also 

 in the latent heat of fusion and of evaporation. 

 The heat of combination of a compound is the 

 same, whether the latter be formed suddenly 

 or by degrees. 



The part played by affinity in these cases is 

 further illustrated by such facts as that, while 

 H and 01, CO and O, &c., combine suddenly 

 in unlimited quantities by means pf the electric 

 spark, and with evolution of heat, in other cases, 

 as N and O, combination by electric action oc- 

 curs gradually, without evolution of heat, and 

 only so long as the spark passes. In the first 

 of these sets of cases, the components have 

 enough of energy, but not of affinity: the elec- 

 tric spark initiates the supply of the latter, 

 which may then be supposed to be kept up by 

 the heat that at once begins to be evolved. In 

 the second, the components are deficient in 

 energy; and electricity furnishes this, each 

 spark yielding only a definite amount of work. 

 The case of ammonia forms an exception as yet 

 unexplained. Finally, the author takes ground 

 against the assumption often made that the 

 heat of combination, in a given case, is to be 

 taken as the measure of the chemical affinity ; 

 and he considers the former, regarded as differ- 

 ence in energy, as being rather the measure of 

 the stability of the compound. 



Constitution of Ammonium Amalgam. This 

 subject is treated of by Dr. Charles M. "Wether- 

 ill, in an article in the American Journal of 

 Science, September, 1865. The author remarks 

 that the existence of the hypothetical radical, 

 NH 4 (ammonium), depends less upon the char- 

 acteristics of its so-called amalgam than upon 

 the parallelism of. its salts with those of the 

 alkalies. But, once admitting the metallic na- 

 ture of ammonium, it is difficult to avoid assign- 

 ing a similar character to the radicals of many, 

 if not all, of the organic bases ; whence, there 

 must be numerous compound metals, and the 

 notion of a metal as an element is destroyed. 



The so-called ammonium amalgam bears a 

 close resemblance in physical properties to the 

 amalgams proper. The mercury in it has lost 

 its fluidity, and its relations of cohesion and 

 adhesion are changed; thus, it has become 

 pasty, and adheres to platinum, iron, and other 

 metals. The mass has also become much in- 

 creased in volume; but left to itself, it grad- 

 ually shrinks, resolving itself again into mercury, 

 and ammonia compounds and hydrogen [NH S 

 (NH 4 0)H]. In reflecting on the questions why 

 ammonium should thus apparently blend with 

 mercury, and then fall apart into NH 8 and H, 

 and why it should unite with the mercury rather 

 than at once oxidize by decomposing the water 

 present, Dr. Wetherill conceived the idea that 

 there is in reality no amalgam of ammonium 

 formed; but that, in the reaction, the sodium 

 decomposes the water, evolving hydrogen, and 

 forming caustic soda, which in its turn sets free 

 ammonia from the chloride, the mercury be- 

 ing also liberated (thus, NH 4 Cl + HO + HgNa= 

 NILO+H+NaCl+Hg); and further, that in 



the so-called amalgam the molecules of mercury 

 have become altered in their capacity for co- 

 hesion, by catalysis, polarity of atoms, or some 

 unknown cause, so that the bubbles of gas are 

 retained, and swelling takes place. 



The author accordingly experimented in a 

 variety of ways upon the ammonium amalgam, 

 obtained by agency of that of sodium. He 

 proved that the change in the mercury was not 

 due to action of nascent hydrogen, whether 

 alone or in presence of ammonia, but only oc- 

 curred when the ammonia itself was in the 

 nascent condition. Among his experiments 

 were that of squeezing the amalgam through 

 a piece of muslin, when it was immediately, and 

 without change of temperature or other evi- 

 dence of affinity, resolved into mercury ; that 

 of forming the amalgam by means of the bat- 

 tery, using different ammonia salts in contact 

 with mercury at the negative pole, &c. "When, 

 upon filter paper placed on a glass plate, and 

 moistened with solution of carbonate of ammo- 

 nia containing lumps of the salt, a globule of 

 mercury is deposited, and the current of a 10- 

 cell Bunsen battery is passed through the mer- 

 cury and paper, the mercury being in contact 

 with the negative pole, the amalgam is finely 

 produced, extending out in dendritic form 

 toward the positive pole ; but if a glass plate be 

 pressed upon the materials so as to prevent the 

 swelling, the amalgam is not formed. 



From the results of his experiments, the 

 author concludes that 1, the so-called am 

 monium amalgam is not an alloy of mercury 

 and ammonium ; 2, the swelling of the mass is 

 due to retention of gas bubbles ; 3, the coher- 

 ence of the gases and liquids concerned is 

 changed from a normal condition, exhibiting 

 phenomena which may be classed with those 

 of catalysis. 



VI. APPLICATIONS OF CHEMISTRY. To some 

 extent, of course, applications of chemical princi- 

 ples and facts, and the processes for obtaining 

 certain elementary and compound bodies, have 

 been incidentally alluded to in preceding por- 

 tions of this article, as well 'as also in others to 

 which, in course of it, reference is made. As 

 properly belonging under this head, for exam- 

 ple, are the articles, sugar and wines. 



Processes for Obtaining Oxygen. Among 

 processes lately proposed for this purpose, that of 

 "Webster is mentioned in this CYCLOPAEDIA for 

 1862. Several others have since been pub- 

 lished. 



Mr. Bobbins has described a process to which 

 he has given the name of "Oxygenesi.s," and 

 which, he states^ furnishes the gas instantane- 

 ously and without the need of applying heat. 

 The method is based on an experiment duo to 

 Schonbein : in it, a dry powdered mixture [ac- 

 cording to one account] of three equivalents of 

 peroxide of barium and one of bichromate of pot- 

 ash, is placed in a glass flask provided with an 

 exit tube; and dilute sulphuric acid being 

 then poured on, oxygen is given off freely and 

 with effervescence. Theoretically, it is con- 



