320 ZINC 



were ashed at 450°C, the ash transferred to squares of blotting paper 

 which were wrapped in cellophane, and the gamma rays measured with a 

 Geiger counter. Fairly large samples of dog excreta were ashed at 450°C, 

 the ash dissolved in HCl, and the insoluble portion re-ashed and redis- 

 solved. Any HCl-insoluble material was measured directly. Aliquots 

 of the HCl solution were treated with ZnCls and K2CO3 to precipitate 

 ZnCOs, which was collected, dried, and counted as above. 



In another study, a cow was given orally 3 mc Zn«^ in 7 mg ZnCl2, and 

 solution counts made on milk and urine (Zn-5) . The distribution in rab- 

 bits of the following Zn^^-labeled compounds was studied: zinc carbonate, 

 zinc phosphate, and zinc dithizone complex. Tissues were prepared for 

 counting by a modification of the dithizone method for chemical analysis 

 (Zn-6). The investigator should establish the necessity for such a com- 

 plicated procedure before using it. 



The uptake by tomato plants of Zn^^ adsorbed onto bentonite was 

 studied (Zn-7). The oven-dry plant material was ashed at 550°C, and 

 the ash spread uniformly on the bottom of seamless tin boxes for counting 

 with an Al absorber of 0.13 g/cm^. Greenhouse studies on the plant 

 uptake of Zn^^ from soils and fertihzers have been described (Zn-8) . As 

 an example of the general procedure, 30 ml of a solution containing 1 g 

 zinc and 0.3 mc Zn«^ both as the chloride, was incorporated into 1 kg of 

 dry sand, which was then stored in a closed glass jar and weighed out as 

 needed at the rate of 10 mg zinc and 3 mc Zn^^ per kilogram of soil. The 

 sand and soil for each pot were thoroughly mixed. For analysis, plant 

 material was dried and ground, and 1- to 2-g samples wet-ashed with 

 HNO3, HCIO4, and H2SO4. The zinc-sand-fertihzer mixture was 

 extracted with 0.1 A^ HCl. The zinc from both types of samples was 

 determined by dithizone methods on ahquots containing 5 to 40 mg zinc. 

 Radioassays were made by pipetting 1 ml of the CCU remaining from the 

 chemical determination into an aluminum pan, evaporating at room tem- 

 perature, muffling at 400°C for an hour to oxidize the dithizone, and 

 counting with an internal counter. 



Zn-1. Vallee, Bert L., and John G. Gibson, 2d: An Improved Dithizone Method for 

 the Determination of Small Quantities of Zinc in Blood and Tissue Samples, 

 J. Biol. Chern., 176: 435-443 (1948). 



Zn-2. Vallee, Bert L., and John G. Gibson, 2d: The Zinc Content of Normal Human 

 Whole Blood, Plasma, Leucocytes, and Erythrocytes, J. Biol. Chern., 176: 



445-457 (1948). . . 



Zn-3. Cowling, Hale, and E. J. Miller: Determination of Small Amounts of Zmc m 



Plant Materials, Ind. Eng. Chern. Anal. Ed., 13: 145-149 (1941). 

 Zn-4. Sheline, G. E., I. L. Chaikoff, H. B. Jones, and M. Laurence Montgomery: 



Studies on the Metabolism of Zinc with the Aid of Its Radioactive Isotope, J. 



Biol. Chern., 147: 409-414 (1943). 



