SANGER AND RIEGEL. — DETERMINATION OF ANTIMONY. 23 



be avoided in the arsenic method by a cotton wool filter, it is necessary 

 to have a much greater degree of saturation in order to obtain compact 

 and uniform deposits on the strips from stibine. If the hydrogen is 

 partially dried by cotton wool before impinging upon the sensitized 

 paper, the bands are long, irregular and not comparable. By increasing 

 the saturation and by making it as uniform as possible we have suc- 

 ceeded in determining the conditions under which the bands are short, 

 regular, and perfectly comparable. 



To effect this and at the same time to hold back any hydrogen sul- 

 phide which might be formed in the reduction, we use disks of lead 

 acetate paper inserted in the straight-walled funnel tube and moistened 

 with a definite amount of water. These disks are of filter paper of 

 medium thickness, cut in quantity by means of a wad cutter or cork 

 borer so as to fit loosely the bore of the funnel tube. They are saturated 

 with normal lead acetate, di'ied, and kept in a well stoppered bottle. 



Procedure. The deposition tube and funnel tube of the apparatus 

 are cleaned and thoroughly dried. A lead acetate disk is then inserted 

 in the funnel tube and moistened with one drop of water, delivered on 

 the centre of the disk, so that the water spreads evenly to the circum- 

 ference. Three grams of uniformly granulated zinc are placed in the 

 bottle, a strip of sensitized paper is slipped wholly within the deposi- 

 tion tube to a definite distance, and the apparatus is put together. 

 Five or ten cubic centimeters of diluted acid (1 to 6 ; normality, about 

 1.5) are then added through the thistle tube and allowed to act for 

 about ten minutes. The acid is then poured off and fifteen cubic 

 centimeters of fresh acid added. This procedure ensures a uniform 

 degree of moisture saturation in the deposition tube, and the absence 

 of arsenic in the reagents and apparatus is assured. The zinc is also 

 rendered more sensitive, and a regular flow of hydrogen is quickly ob- 

 tained on the second addition of acid. 



In five minutes after this addition, the solution to be tested is intro- 

 duced, either wholly or in aliquot part, which may be determined by 

 weighing or measuring. In case it were necessary from the nature of 

 the analysis to prove the absolute freedom of the apparatus and 

 reagents from arsenic and antimony before adding the solution, the 

 evolution of hydrogen would be continued for a longer time and the 

 strip developed. The absence of contamination being thus assured, a 

 fresh strip would be substituted before adding the solution to be tested. 

 In ordinary work, however, this precaution is quite unnecessary. 



After the solution is introduced, the reduction is continued for 30 

 to 40 minutes. No effect on the sensitized paper is observed unless 

 the amount of antimony added is above 70 mmg., when a slight gray 



