CHEMICAL SCIENCE. 191 



Having now obtained an extremely thin film of gold upon a plate 

 of glass (and that it is continuous and metallic has been anrjoly proved 

 by Faraday), let us see how far it is possible to subdivide it by me- 

 chanical means. From an examination of Nobert's test pfate, it is 

 seen that it is possible to rule lines with a diamond point on glass so 

 close together that upwards of 90,000 of them are comprised in the 

 space of one inch. The apparent limit of vision in the best micro- 

 scopes, as tested by De la Rue, Quekett, and Ross, does not, however, 

 roach beyond lines separated g-o^Q-g- of an inch. Let us, therefore, 

 cut our square inch of gold on the glass plate with lines this distance 

 apart, and crossing each other at right angles. The whole inch will, 

 therefore, be divided into 6,400,000,000 squares, each of which is 

 capable of being distinctly seen under adequate microscopic power. 

 What now is the weight of each piece ? The square inch of gold 

 weighed at the commencement Jy of a grain. By the action of cyan- 

 ide of potassium it was diminished in thickness until it only weighed 

 g- 1_ of a grain. This has now been cut up into 6,400,000,000 separate 

 pieces, each of which, therefore, weighs no more than -g-^oooooooooo 

 of a grain ; or, in other words, a single grain of gold - - a fragment 

 about as large as a good sized pin's head - - has been divided into 

 three billion eight hundred and forty thousand million separate 

 piece?, each distinctly visible to the eye ! 



The mind is quite unable to attach any definite significance to these 

 figures without artificial assistance ; but it may, perhaps, enable our 

 readers to form some faint idea of the minuteness of the subdivision, 

 when we state that each square bears about the same proportion to 

 the original grain of gold that a thimbleful of water does to a building 

 five times the size of St. Paul's. How insignificant do our ideas of 

 great and small appear in the contemplation of such overwhelming 

 figures as these ! In the eloquent words of Dr. Nichol, " Great and 

 little, in truth, seem in creation alike terms expressing merely rela- 

 tion to us, and vanish in the universe of the infinite God." , 



DETECTION OF 1-10,OOOTH OF A MILLIGRAMME OF QUINIA. 



M. Flucker, of Geneva, calls attention to the fact that by means of 

 the fluorescence of sulphate of quinia in solution we may be able to 

 indicate the presence of this substance in most wonderfully minute 

 quantities. " One is able," he says, " to discover through the reaction 

 of ammonia and prussiate of potash - 8 ^ to Yo7ro"o" ^ c l um i a - When 

 sulphuric acid is in excess, the fluorescence is observable if there be 

 but ^-croVoo" f quinia present, when you fill a common test tube with 

 the solution, expose it to the sunlight, and hold a piece of black paper 

 against it. At a higher dilution, the fluorescence disappears to the 

 eye altogether, but it becomes visible at once if a pencil of rays is 

 made to fall vertically, or even obliquely, through the tiibc, when the 

 outline of the converging rays is clearly observable, when the solu- 

 tion of sulphate of quinia contains only -g-o^VoT ^ a!kaloid. Yet this 

 reaction is so extremely acute, that by very favorable light and a 

 careful manner of proceeding (strong magnifying tube of the utmost 

 possible focal distance, pure white glass, and* dark background), the 

 * so^ooo becomes visible. In this way one can absolutely 



