No abstract

It is possible to determine 2.5 to 250 y of mercury photometrically by extracting the mercury salt solution with an excess of dithizon solution in chloroform and measuring the extinctions of the chloroform layer a t 500 and 610 mp. T h e amount of mercury is calculated from the volume of dithizon solution used and the extinctions E, and E,,, measured, thus standardization of the dithizon solution is unnecessary.%he pure solution of the orange coloured mercury dithizonate in chloroform turns a dirty greenish orange in daylight, in direct sunlight it becomes bluish purple in a few minutes. T h e original colour is quickly recovered again in the dark. This reversible photochemical process is completely inhibited by acetic acid.For the quantitative determination of small quantities of mercury the use of dithizon ( D z ) is at present preferred. W i t h this substance the mercury can be determined according to two principles 1 ) . by titration and by so-called mixedcolour colorimetry. Photometric methods do not seem to be in use, which is surprizing when it is kept in mind that f o r the determination of lead, copper and zinc with dithizon photometric methods are much preferred. During the years 1935-1939 W i n k 1 e r did attempt to determine mercury quantitatively by means of the extinctions of mercury dithizonate (HgDz,), but he later declared his own method to be useless,), due to the instability of the compounds when exposed to light. A photometric method was proposed by F i s c h e r and L e o p o 1 d i 3 ) ; no experience of this method by other investigators is however known, and it seems to us to be more laborious than the new method described below.Our method can be explained as follows. W h e n a solution of a mercuric salt in dilute sulphuric acid is shaken with the green solution of Dz in chloroform, HgDz, is formed and dissolves in the chloroform forming an orange solution. (In this mineral acid medium only-gold and platinum may constitute a hindrance). W i t h a slight excess (5-10 percent) of Dz, which is manifested by a dirty greenish orange colour of the chloroform layer, the complete extraction of the mercury is insured. If it is permissible to apply the law of L a m b e r t -B e e r to this solution, the concentrations c,)~ and clIF of the two coloured substances Dz and HgDz, can be calculated from the extinctions at two wave *lengths chosen as suitably as possible, namely that wave length at which the light absorption by the Dz is relatively the greatest and that wave length at which the light absorption of the Dz is relatively the smallest compared with that of the HgDz,.In order to work out this principle we determined the extinction curves of

No abstract

No abstract

No abstract