ANALYTICAL CHEMISTRY
124 for niekcl in iron and s t t d :is when dimet,hylglyoxinrr ir uscd ( 1 ) . If an insoluble residue rcinnins, it is fikrred ON:tnd sashed thoroughly with hot mater. If this rcsidur is suriprrterl oi containing nickel, the paper is hurncd, t r e n t d with hydroRuoriistill for 7 t o 8 millute., removc he:it from flask, and draw off distillate into :t 25-1111. volumc~tric,fla6k. K a s h the trap with sm;ill portionr of \v:ii-ni rc~lic~illcd \v:itrr and collect thcsc in the voliimrtric f h s k . It i- niuc,h rinipler :tnd emier to wash out this ati~i~rptiori tr:iri , i f : c - r . i ~ i c . 1 1~1istiIl:~tion than to wash the trap on
C.
the Riggs-Chancy still. The distillate volume is made up-to 25 ml. when aliquots are taken for the colorimetric determination of iodide by its catalytic effect on reduction of cerate in the presence of excess arsenite. The float valve is merely a thin-walled hollow glass sphere with a short tail. The capillary water return is 6 cm. long and is turned up 2 cm. Its inside diameter is 1 to 2 mm The entire still w a ~ made by one of the authors (H.G.W.). Details of other techniques and procedures have been sdequately described ( 2 , 3 ,8). LVith one exception all samples of C.P. chromic acid that were tried contained too much iodine for this procedure. However, a sample of Grasselli’s technical grade was found t o be sufficiently low in iodine (approximately 0.05 microgram per gram). GreenTo W a t e r
Condenser
9
3
Absorption Trop
3
-
Funnel
I I 1 I 1
To D i g e s t i o n Distillation
Flosk
Figure 1.
Reflux Distillation Apparatus
