102 



sir W. Roberts-Austen. 



tin- l>ases of the cylinders by means of clamps. The lal>oratory in 

 which the cylinders were placed consists of a vaulted chamber situated 

 in the basement of the Mint, and its temperature varied but little from 

 a mean of 18 C. The diameters of the cylinders were in all cases 

 0*88 c.m., their lengths varied somewhat, the longest being 25 cm. 

 At the end of the four years the discs of gold were found to be 

 adherent to the lead. The cylinders were divided into thin slices at 

 right angles to the axes of the cylinders, the first slice was approximately 

 0'75 mm. thick, but the succeeding layers were about 2'3 mm. thick. 

 By the ordinary methods adopted by assayers, which were conducted 

 with extraordinary precautions, gold wsis found in each of the four 

 lower slices, while only the minutest traces of gold could be found in 

 any slice beyond the fourth from the base. The amount of gold 

 that had diffused in the different cylinders of lead was, however, not 

 uniform. The variation is probably due to difference in contact 



Gold Spangles. 

 4th layer. 



Gold Globule. 

 3rd layer. 



Gold Globule. 

 2nd layer. 



Gold Globules. 

 1st layer. 



ft 



between the cylinders of lead and the discs of gold. The results in 

 all four experiments were, however, of the same order, and it will 

 be sufficient to give the actual amounts of gold found in a single 

 cylinder. The richest layer was, of course, the one in direct contact 

 with the gold, and from it a globule of gold was extracted which 

 weighed 0*00005 gramme. There is in the Mint a balance that will 

 readily weigh such globules. The gold extracted from the 2nd and 3rd 

 layers was too small to be weighed, but the amounts could be approxi- 

 mately determined by measurement under a microscope. Actual 



