Maxson — Determination of Small Amounts of Gold. 273 



diameter of l cra and a length of 13 cm , and were accurately 

 graduated to hold I0 cm \ 



A mirror suitably situated beneath the box containing the 

 tubes gave efficient illumination. Such an apparatus is not 

 only cheaply and easily procured, but if tubes of these dimen- 

 sions are used it is capable of accurately determining very 

 small amounts of gold. 



The method of comparison was carried out in the following 

 manner. A measured amount of the suspension was drawn 

 off into the left hand tube and diluted to the mark with water ; 

 a suitable amount of water was then placed in the right hand 

 tube and the standard suspension drawn into the tube until 

 the colors were seen to be identical. The necessary amount of 

 water to be used can be determined by preliminary experiment. 



The positions of the tubes were always reversed before the 

 final reading was taken. 



The following experiments were made in order to determine 

 the error and range of amounts of gold capable of accurate 

 estimation in such an apparatus with tubes of the dimensions 

 described above. The comparisons were made with a red sus- 

 pension prepared by careful dilution of a more concentrated 

 standard suspension which contained p-000010175 grams of 

 metal in one cm 3 . 



The results obtained with different concentrations of the 

 standard suspension just described are given in the following 

 table. 









Table II. 









Gold sus. 



Gold sus. 









No. 



taken. 



used. 



Gold used. 



Gold found. 



Error. 



Ana. 



cm 3 . 



cm 3 . 



grm 



grm. 



grm. 



1 



9-50 



905 



0-000102 



0-000097 



— 0-000005 



2 



8-00 



7-59 



0-000086 



0-000082 



— 0-000004 



3 



7-00 



0-89 



0-000075 



0-000074 



—o-oooooi 



4 



6-00 



5-83 



0-000065 



0-000063 



— 0-000002 



5 



5*00 



4-84 



0-000054 



0-000052 



— 0-000002 



6 



4-00 



3-88 



0-000043 



0-000042 



— 0-000001 



7 



3-00 



2-47 



0-000032 



0-000027 



— 0-000005 



8 



2-00 



1-82 



0-000022 



0-000020 



— 0-000002 



9 



1-00 



0-93 



0-000011 



o-ooooio 



—o-oooooi 



The intensity of the color in the above experiments ranged 

 from a deep red to a faint pink. Further comparisons made 

 with suspensions more dilute than those described above gave 

 errors of magnitude increasing with the dilution. The amounts 

 handled here are, then, the minimum quantities that can be 

 accurately estimated with the apparatus described. It is obvious 

 that if larger amounts of the metal are to be determined, tubes 

 of greater dimensions should be used. 



