72 
Proceedings of the Royal Society of Edinburgh. [Sess. 
570 and 528 and then slowly increasing absorption in the bine and violet, 
was mixed with an ammoniacal solution of copper sulphate. The strength 
of the carmine solution was 0T5 gms. per litre. The strongest copper 
sulphate solutions had about 10 gms. copper sulphate per litre. Strengths 
down to d^nd of this were used. A definite shift of both bands to the red 
was obtained, amounting as a rule to 20 Angstrom units which seemed to 
remain pretty much the same as the concentration of the copper sulphate 
was diminished. The measurements were always made on the centre of 
the bands. The bands were so ill-defined that 10 Angstrom units was the 
smallest shift one could be sure about. In this case there is nothing to 
show whether the change is physical or chemical. 
The effect was tried next of mixing the ammoniacal solution of carmine 
with potassium dichromate. The strength of the latter solution was 4 gms. 
per litre and less. We could not say whether there is a shift to the violet 
or not. If there is one it cannot be more than 5 Angstrom units. But 
there is no doubt whatever that the ammonia acts on the dichromate, 
changing it into the chromate, and pushing back the beginning of the 
continuous absorption much further into the violet. Bostwick, it must be 
o 
noted, obtained a definite shift in both cases of the order of 40 Angstrom 
units. It is difficult to say what the discrepancj^ is due to. We varied our 
conditions repeatedly but cannot explain it. 
We finally repeated some of Formanek’s experiments. Here we had 
trouble with the cells. The cement absorbed the aniline dyes used, some- 
times rapidly, sometimes just appreciably. Cells made by Leybold, cells of 
unknown manufacture, and home-made cells were alike unsatisfactory ; and 
cells made without cement, of plate glass held together with rubber bands, 
leaked. It was therefore necessary, to do the work thoroughly, to have 
cells made without cement by R. & J. Beck, Limited, with first quality 
glass surfaces, the different pieces being kept together by a brass frame. 
The figures show how this was done. The cells were double and were used 
