24 PROCEEDINGS OF THE AMERICAN ACADEMY. 



color may appear. Larger amounts Would turn the paper still darker. 

 If any color appears, it is an indication that the amount will be difficult 

 to estimate, and hence another trial should be made with a smaller 

 portion of the solution, or from less of the original substance. 



The strip is now placed in a test tube and covered with normal 

 ammonic hydroxide, which is allowed to act for five minutes'. A black 

 band is slowly developed, somewhat duller and considerably shorter 

 than would be obtained from the same amount of arsenic, the latter 

 difference being chiefly due to the moisture conditions in the deposi- 

 tion tube. The band is then compared with a set of standard bands. 

 The amount of antimony in the entire solution follows from that deter- 

 mined in the aliquot part. 



Standard Bands. A standard solution is made from pure, recrys- 

 tallized tartar emetic, shown to be free from arsenic. 2.3060 grams 

 are dissolved in water and made up to one liter. This solution (I) 

 contains 1.0 mg. of antimonious oxide per cubic centimeter. From 

 this, by dilution, are made two solutions containing respectively 0.01 

 mg. (II) and 0.001 mg. (Ill) per cubic centimeter. From definite por- 

 tions of solutions II or III a series of bands is made by the above 

 procedure, using a fresh charge of zinc and acid for each portion. The 

 lower half of the Plate shows the actual size and shading of the set of 

 bands, corresponding to the following amounts of antimonious oxide in 

 micromilligrams : 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70. 



These bands have shown a fair degree of permanency, but fade slowly 

 on exposure to moisture and light. They may be sealed in glass tubes 

 with quicklime, if desired, as in the case of the corresponding ammonia- 

 developed arsenic bands, but we have found it sufficient to mount them 

 on a dry glass plate, which is covered by a dry plate of the same size. 

 The two plates are then cemented together and bound with passepar- 

 tout paper. The set thus mounted, if kept in a desiccator away from 

 the light, will last for some time. In case a fresh set of standards is 

 not available, a band may be approximately estimated from the accom- 

 panying Plate ; the more accurate determination being made, if neces- 

 sary, by comparison with freshly prepared bands from selected 

 amounts. 



Analytical Notes. 



General Precautions. As in the arsenic method, the solution to be 

 reduced should contain no interfering organic matter, except that any 

 oxide of antimony obtained in the preparation for analysis may be 

 eventually dissolved in tartaric acid. Sulphur in any form reducible 

 to hydrogen sulphide should be removed as completely as possible, but 



