( 273 ) 
Chemistry. — “The alleged identity of red and yellow mercuric 
ovide’, Part I. By Dr. Ernst Conen. (Communicated by 
Prof. H. W. Baxuuis ROOZEBOOM.) 
1. Some years ago, (1895), in a review ') of Varets’ thermo- 
chemical determinations 2) concerning red and yellow mercuric oxide, 
OsTWALD said that in his opinion it was doubtful whether the two 
modifications were isomeric. He added the remark: “probably they 
only differ in the size of their particles, that is mechanically”. 
Shortly after this review, OstwaLp published the results of some 
measurements %), made at his request by THor Mark with the 
object of seeing whether we are here confronted by a case of identity 
or isomerism. 
OstWaLD concluded that “the two kinds of mercuric oxide are 
no more different than crystallised and powdered potassium bichro- 
mate, which exhikit a similar difference of colour; they are not 
isomeric but identical’. 
This conclusion rests on the following experiment: a galvanic 
cell, arranged as follows: 
! 
| Red oxide | Yellow oxide | 
Mercury | in potash solution | in potash solution | 
Mercury 
showed, according to MARK’s measurements, a difference of po- 
tential of less than 0,001 volt, since, as OstwaLD said „no deflec- 
tion could be observed with the electrometer used which was capable 
of measuring 1 to 2 millivolts”. 
Besides this electrometric determination of solubility, determinations 
of the solubility of the two oxides in solutions of potassium bromide, 
potassium iodide and sodiumthisosulphate were made. After satura- 
tion, the solutions, which had become alkaline *), were titrated with 
hydrochloric acid. Equal volumes of the solutions required the 
following quantities of acid: 
Potassium bromide Potassium iodide Sodiumthiosulphate 
solution saturated with solution saturated with solution saturated with 
Red oxide Yellow oxide Red oxide Yellow oxide Red oxide Yellow oxide 
6,16 eem. HCl. 6,20 eem. HCI. 49,82 eem. HCl. 49,64 eem. HCl. 51,84 eem. HCl. 51,98 eem. HCl. 
51,75 Fae) A ee 
DL Sieve 6 ete oe 
1) Zeitschrift für physikalische Chemie 17. 183 (1895). 
2) ©. R. 120. 622 (1895)., Ann. de chim. et de phys. (7) 8, 79 (1896). 
5) Zeitschrift fiir phys. Chemie 18, 159 (1895). 
‘) Berscu, Zeitschrift fiir phys. Chemie 8, 383 (1891). 
