302 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Standard Color Bands. A standard solution is made by dissolving 

 one gram of re-sublimed arsenious oxide in a small quantity of sodic 

 hydroxide free from arsenic, acidifying with sulphuric acid and making 

 up to one liter with recently boiled water. Of this solution (I) 10 c.c. 

 are diluted to a liter with freshly boiled water, giving a solution (II) 

 which contains 0.01 mg. or 10 micromilligrams (mmg.) of arsenious 

 oxide per cubic centimeter. In testing the delicacy of the method we 

 have also prepared solutions containing 1 mmg. (Ill) and 0.1 mmg. 

 (IV) per cubic centimeter. 



From definite portions of solution II, measured from a burette, a 

 series of color bands is made by the above procedure, using a fresh 

 charge of zinc and acid for each portion. Figure 1 (Plate 1) shows in 

 colors the actual size of the set of bands made by us, corresponding to 

 the following amounts of arsenious oxide in micromilligrams: 2, 5, 

 10, 15, 20, 25, 30, 35, 40, 50, 60, 70. The color in the lowest values 

 is a lemon yellow, shading from this to an orange yellow and through 

 orange yellow to reddish brown in the higher values. 



Preservation and Development of the Color Bands. The rapid fading 

 of the stains has been a serious obstacle to the use of the Gutzeit re- 

 action for a quantitative method, and it became very soon evident to 

 us that some means of preserving the color bands must be found before 

 the method could be considered an entirely practical one. It was 

 clear that the chief factors in the change of color were light and mois- 

 ture, the latter being by far the more important. Concerning the 

 mechanism of the reactions, either for the formation of the color or for 

 its decomposition with water, the work of those who have investigated 

 the reactions was not sufficient to guide us. 



The early work of Rose ^ on the action of arsine on excess of mer- 

 curic chloride in solution showed that a yellowish brown precipitate 

 was formed having the empirical formula AsHgsCls. This was con- 

 sidered by Rose to be made up of mercurous chloride and a compound 

 of mercury and arsenic, to which the formula As2Hg3 might be given. 



Mayen^on and Bergeret ^° consider the compound to be a ijiixture 

 of arsenic and mercurous chloride. 



Franceschi,^! apparently without knowledge of Rose's work, passed 

 arsine through an aqueous solution of mercuric chloride. The liquid 

 became at first a light yellow, then red, and there was precipitated a 

 substance at first yellow, but with excess of gas a dark red, "of the 



9 Pogg. Annal., 51, 423 (1840). 

 " Comptes Rendues, 79, 118 (1874). 

 " L'Orosi, 13, 289 (1890). 



