抄録
The part which zinc plays in organisms have been shown by several authors such as MENDEL and BRADLEY, 1) who found that zinc in Sycotypus canalicalatus is an essential constituent of the respiratory protein, “hemosycotypin”, RAULIN2) and JAVILLIER, 3) who confirmed the favorable stimulatory influence of minute quantities of zinc on the growth of some micro-organisms. BIRCENER4) has estimated the zinc content of a number of food products. BODANSKY5) and SEVERY6) made a study of zinc content of several different marine animals.
In the nephelometric method of zinc analysis FAIRHALL and RICHARDSON, 7) determined recently the most favorable condition in respect of the acidity, the salt concentration or the time of standing, for the development of opalescence of zinc ferrocyanide. Taking these favorable condition, into account, the present author have made a little modification for the separation of zinc from other metals such as iron, manganese and copper, which constantly occur in the biological material and interfere the opalescence of zinc ferrocyanide. Excess of NaOH in the presence of NH4Cl gives gelatinous precipitates of the above three metals, but does not of zinc hydroxide. The modified method, which is based upon this fact, is as follows :
Dissolve the ash of biological material obtained by heating with cone. H2SO
4 and 30% H2O2 in a little HCl and hot water. Transfer it into a cylinder and add a few drops of saturated NH4Cl solution and excess of cone. NaOH solution, until no more gelatinous pre-cipitate is evolved. After standing a few hours, filter the metal hydroxide off. Wash well the precipitate with NaOH solution. Concentrate the all filtrate to about 20 c.c. Filter again if necessary. Add excess of SH2 containing water and heat in boiling water for just 10 minutes. Filter out the zinc sulfide and wash well with SH2 containing water. Dissolve the sulfide in 2 c.c. of n HCl. Transfer it to a 25 c.c. mess-cylinder filling to about 20 c.c. by distilled water. Then add 1 c.c. of 1% K4Fe(CN)6. Fill up by distilled water to a mark and mix it well. Compare after 20 minutes the turbidity thus evolved in a nephelometer with a standard, containing 0.5mg of zinc, treated just the same as sample. The acidity of the resulted solution is 10-2.3, at which the max. of opalescence of Zn-ferrocyanide appears. The salt concentration, like as KCl, also influences the opalescence, but in this case it may be disregarded, as its concentration becomes always constant. Standard solution was made by dissolving 0.3724g. of well dried zinc lactate in a little quantity of HCl and filling up to 1 litre by dis-tilled water, 1 c.c. of the solution contains 0.1mg. of Zn. The blind test is always necessary. Results are presented in Table 1, showing the recovery of zinc from solutions containing known amount of this element.
By using the foregoing method the zinc content of ten kinds of food-organisms for fish mentioned in previous papers (I, II) was analyzed and the data is summarized in Table 2.
