42 Brown — Work on the Interaction of Hydrochloric Acid. 



chloride also contained iron. This was removed by heating; 

 with a strong solution of oxalic acid, filtering; off the gold thus 

 precipitated, and washing; until free from iron and oxalic acid. 

 The gold was then dissolved in aqua regia, and the excess of 

 nitric and hydrochloric acids removed as with platinum. 



Wagner* states that in experimenting with the various 

 metallic chlorides which he regards as catalyzers, he used tenth- 

 normal solutions of the same content in chlorine. This with 



19*5 

 chlor-platinic acid would mean a solution containing — = — = 3-25 



grams of platinum to the liter since chlor-platinic acid con- 

 tains six atoms of chlorine to the molecule. With chlor-auric 



19'73 

 acid it means =4-9322 grams of gold to the liter since 



chlor-auric acid contains four atoms of chlorine to the mole- 

 cule. . Similarly tenth-normal solutions of chromic chloride, 

 cadmium chloride, and ferric chloride must contain 1"7366 

 grams chromium, 5*6 grams cadmium, and 1*8666 grams iron, 

 respectively. The solutions used in the experiments about to 

 be described were standardized in this way in respect both to 

 chlorine and metal, and in no case showed a noticeable excess 

 of chlorine, the excess never exceeding the equivalent of one 

 or two hundredths of a cubic centimeter of normal hydro- 

 chloric acid. 



Experiments were then conducted in the following manner : 

 To a 300 cm3 flask were added 100 cm3 of normal hydrochloric acid, 

 and in addition either 9*90 cm3 of tenth-normal ferric chloride, 

 cadmium chloride, chromic chloride, chlor-platinic acid, or 

 chlor-auric acid. Of approximately twentieth-normal potas- 

 sium permanganate 9 , 90 ctn3 were then added, and the flask fitted 

 in a ground joint to a return condenser approximately 60 cm3 in 

 length, was heated for one hour, or thirty minutes, on the 

 Ostwald thermostat at a temperature of 50° C. Of approxi- 

 mately tenth-normal oxalic acid 9"90 cm3 were then added, and 

 permanganate run in to color. Calculations of the amount of 

 permanganate " apparently reduced " were then made by sub- 

 tracting the permanganate equivalent of the oxalic acid from 

 the total permanganate used, (that is the "KMn0 4 before diges- 

 tion" plus the u KMn0 4 to color.") Similarly the " KMn0 4 

 apparently unreduced " is obtained by subtracting the " KMn0 4 

 apparently reduced " from the " KMn0 4 before digestion." 



* Loc. cit., p. 85. 



