January ;^o, 1908] 



NATURE 



307 



conceiving that, as the volatile alkali was composed of the 

 light inflammable hydrogen united to nitrogen, so the fixed 

 and denser alkalis might be composed of the denser in- 

 flammable bodies — phosphorus and sulphur — also united to 

 nitrogen. 



Davy once said that " analogy was the fruitful parent 

 of error," and few more striking instances of perverted 

 analogy are to be met with in science than this. In 

 another of his lectures he said of the alchemists that 

 " even their failures developed some unsought-for object 

 partaking of the marvellous " ; and if such had been his 

 reasoning, the statement is no less true of himself. 



So far as can be ascertained, it was on October iq, 

 1807, that he obtained his first decisive result. This is 

 thus described in Davy's own handwriting in the Labora- 

 tory Journal, which has been preserved for us by the pious 

 care of Faraday, and which is one of the most precious 

 of the historical possessions of the Royal Institution : — 

 " When potash was introduced into a tube having a 

 platina wire attached to it, so [fig.], and fused into the 

 tube so as to be a conductor — i.e. so as to contain just 

 water enough, though solid — and inserted over mercury, 

 when the platina was made negative, no gas was formed 

 and the mercury became oxydated, and a small quantity 

 of the alkaligen was produced round the platina wire, as 

 was evident from its quick inflammation by the action of 

 water. When the mercury w-as made the negative, gas 

 was developed in great quantities from the positive wire, 

 and none from the negative mercury, and this gas proved 

 to be pure oxygen — a capital experiment, proving the de- 

 composition of potash." On the iqth of the following 

 month he delivered what is generally regarded as the most 

 memorable of all his Bakerian lectures. It is entitled 

 " On some New Phenomena of Chemical Changes produced 

 by Electricity, Particularly the Decomposition of the Fixed 

 Alkalies ; and the E.xhibition of the New Substances which 

 Constitute their Bases ; and on the General Nature of 

 Alkaline Bodies." 



Few discoveries of like magnitude have been made and 

 perfected in so short a time, and few memoirs have been 

 more momentous in result than that which, put together 

 in a few hours, gave the results of that discovery to the 

 world. 



The whole work was done under conditions of great 

 mental excitement. His cousin, Edmund Davy, who at 

 the time acted as his assistant, relates that when he saw 

 the minute globules of the quicksilver-like metal burst 

 through the crust of potash and take fire, his joy knew 

 no bounds ; he actually danced about the room in ecstasy, 

 and it was some time before he was sufficiently composed 

 to continue his experiments. 



The rapidity with which he accumulated results after 

 this first feeling of delirious delight had passed was extra- 

 ordinary, and he had obtained most of the leading facts 

 concerning the physics and chemistry of the new sub- 

 stances before the middle of November. 



He began his lecture with a felicitous reference to the 

 concluding remarks of the one of the previous year, 

 namely, " That the new methods of investigation promised 

 to lead to a more intimate knowledge than had hitherto 

 been obtained concerning the true elements of bodies. This 

 conjecture, then sanctioned only by strong analogies, I am 

 now happy to be able to support by some conclusive facts." 



In the first attempts he made to decompose the fi.xed 

 alkalis he acted upon concentrated aqueous solutions of 

 potash and soda with the highest electrical power he could 

 then command at the Royal Institution, viz. from voltaic 

 batteries containing twenty-three plates of copper and zinc 

 of 12 inches square, too plates of 6 inches, and 150 of 

 4 inches, charged with solutions of alum and nitric acid ; 

 but although there was high intensity of action, nothing 

 but hydrogen and oxygen was disengaged. He next tried 

 potash in igneous fusion, and here the results were more 

 encouraging; there were obvious and striking signs of 

 decomposition ; combustible matter was produced, accom- 

 panied wilh flame and a most intense light. He had 

 observed that although potash, when dry, is a non-con- 

 ductor, it readily conducts when it becomes damp by 

 exposure to air, and in this state " fuses and decomposes 

 by strong electrical powers." 



NO. T996, VOL. 77] 



Let me state in his own words, for the words are 

 classical, what followed ; — - 



"A small piece of pure potash, which had been exposed 

 for a few seconds to the atmosphere, so as to give con- 

 ductive power to the surface, was placed upon an insulated 

 disc of platina, connected with the negative side of the 

 battery of the power of 250 of 6 and 4 [that is 100 plates 

 of 6 inches square and 150 plates of 4 inches square] in 

 a state of intense activity ; and a platina wire com- 

 municating with the positive side was brought in contact 

 with the upper surface of the alkali. . . . Under these 

 circumstances a vivid action was soon observed to take 

 place. The potash began to fuse at both its points of 

 electrization. There was a violent effervescence at the 

 upper surface ; at the lower, or negative surface, there was 

 no liberation of elastic fluid ; but small globules, having 

 a high metallic lustre, and being precisely similar in 

 visible characters to quicksilver, appeared, some of which 

 burnt with explosion and bright flame, as soon as they 

 were formed, and others remained, and were merely 

 tarnished,. and finally covered by a white film which formed 

 on their surfaces." 



He goes on to sav : — • 



" Soda, when acted upon in the same manner as potash, 

 exhibited' an analogous result; but the decomposition 

 demanded greater intensity of action in the batteries, or 

 the alkali was required to be irt much thinner and smaller 

 pieces. 



" The substance produced from potash remained fluid at 

 the temperature of the atmosphere at the time of its pro- 

 duction ; that from soda, which was fluid in the degree of 

 heat of the alkali during its formation, became solid on 

 cooling, and appeared having the lustre of silver." 



It would seem from this description of its properties 

 that the potassium Davy first obtained was alloyed with 

 sodium owing to the fact that the potash contained soda. 

 Potassium is solid up to 143° F., whereas, as Davy was 

 the first to show, an alloy of potassium and sodium is 

 fluid at ordinary temperatures. 



On account of their alterability in contact with air, 

 Davy had considerable difficulty in preserving and con- 

 fining the new substances so as to examine their proper- 

 ties. .As he says, like the alkahests imagined by the 

 alchemists, they acted more or less upon almost every 

 body to which they were exposed. Eventually, he found 

 they might be preserved in mineral naphtha. 



The " basis " of potash was described by him as a soft 

 malleable solid with the lustre of polished silver. 



" At about the freezing point of water it becomes harder 

 and brittle, and when broken in fragments, exhibits a 

 crystallised' texture which in the microscope seems com- 

 posed of beautiful facets of a perfect whiteness and high 

 metallic splendour. It may be converted into vapour 

 below a red heat, and may be distilled unchanged, and is 

 a perfect conductor of heat and electricity. Its most 

 marked difference from the common run of metals is its 

 extraordinary low specific gravity." At the time of its 

 discovery it was the lightest solid known. 



The " basis " of soda was found to have somewhat 

 similar properties. It was slightly heavier than the 

 " basis " of potash, and fused at a higher temperature. 



Davy next examined the behaviour of the new sub- 

 stances towards a large number of reagents, but as his 

 observations are now the common property of the text- 

 books, it is unnecessary here to dwell upon them. 



He then enters upon some general observations on the 

 relations of the " bases " of potash and soda to other 

 bodies : — 



" Should the bases of potash and soda be called metals? 

 The greater number of philosophical persons," he says, 

 " to whom this question has been put, have answered in 

 the affirmative. They agree with metals in opacity, lustre, 

 malleability, conducting powers as to heat and electricity, 

 and in their qualities of chemical combination. 



" Their low specific gravity does not appear a sufficient 

 reason for making them a new class ; for amongst the 

 metals themselves there are remarkable differences in this 



respect In the philosophical division of the classes 



of bodies, the analogv between the greater number of 

 properties must always' be the foundation of arrangement. 



