J. C. Blake — Colloidal Gold. 



383 



Vol. of 

 gold 



sol. 



Precipi- 

 tant. 



Wash 

 water 



Table I. 



Calc. amt. 

 Mixed p, .-, -Ro/nTT\ of Ba(0H)2 Error of 



coagulum, j«°^^ Ba(OH), i,o-5cm» analysis. 

 Ignited, .«<.4.„„^- ™ 



grm. 



supernatant grm. 

 » ^ liquid, grm. 



50 cm 



550 n ^ ,„^ , i ^?^ 

 --Ba(N03),| 50 



10 



100 cm' 

 1200 n~BaC\ 



0-4151 0-4151 0-0000 



500 

 100 



100 2-2668 * 0-0020 



10 cm' f Not "1 



610 71 ^ ^, \ washed. | 0-'7569 07566 0-0000 

 Y0-^'^^^\ Dried 



j between [ 



610 ^^^tS"^I, ! ^^^^^ ! 0-6499 0-641'7 0*0066 0-0060 0-0016- + 

 72—BaC\^ I papers. J 



0-0003 0-0000 



0-0033 



0-0001 0-0003' 



From the foregoing results it is plain that ver}^ little of the 

 barium compound is held by the gold under these conditions, 

 and that the traces thus retained cannot readily be washed 

 out — a condition agreeing exactly with what would be ex- 

 pected if the barium were held as nitrate or chloride dissolved 

 in the liquid mechanically retained by the spongy gold. The 

 obvious physical properties of this spongy gold proved to be 

 identical with those of the gold thrown out from strong solu- 

 tions of gold compounds by ferrous sulphate or oxalic acid, 

 which is known to be crystalline. :j: 



II. The Blue Form of Gold. 



In the following experiments the gold chloride used in pre- 

 paring the colloidal gold solution was all reduced, and the 

 colloidal gold, precipitated with a solution of a barium com- 

 pound, came down in the non-coherent blue form. In the experi- 

 ments given under A (p. 386), the coagulum was washed suc- 

 cessively by decantation with the given amounts of hot water 

 without the use of a filter, part of the finely-divided gold thus 

 temporarily re-suspended being washed away. In the experi- 

 ments given under B, the coagulum was thrown upon an ash- 

 less filter (or asbestos felt) field in a large platinum cone, the 

 mother liquor was exhausted by suction, and the barium com- 

 pound held by the unwashed gold and the filter was determined. 



* Grold lost by explosion, presumably owing to tbe formation of a hydride 

 during reduction by magnesium. 



f This error becomes •0008 — if the barium held by the gold be calculated 

 as the chloride. 



X Eoscoe and Schoelemmer, Treatise on Chemistry, 1898, ii, p. 399. 



