244 Proceedings of Royal Soeiety of Rdinburgli, [march 19 , 
biniodide solution before the blood is put in, there is still no pre- 
cipitate formed, all the reactions are just those above noted, and the 
same series of reactions are still obtained on the addition of 7 c.c. 
of the salt solution to the mixture of mercurial salt and blood. 
If 3 c.c. of a saturated solution of sodium phosphate be added, the 
reactions are still much the same, and haemoglobin may still be 
detected in considerable quantities by means of the spectroscope, 
the red colour of the blood also being retained. 
3 c.c. of a 25 per cent, solution of caustic potash added to the 
biniodide solution gives no precipitate, and when the blood is added 
the fluid first becomes slightly milky or muddy, but after this there 
is evidently rapid reduction of the haemoglobin, for the fluid is 
rapidly cleared up and assumes first a dark red colour, and latterly 
becomes almost black. The haemoglobin absorption bands have, at 
the same time, disappeared from the spectrum. 
If 7 drops of tartaric acid be added to the biniodide and blood 
solution, the mixture immediately assumes a darker colour, which 
gradually deepens until within a few minutes it becomes as black 
as porter. The haemoglobin is completely reduced. At the end 
of twenty-four hours there is a distinct dirty brown gelatinous 
deposit at the bottom of the glass jar, occupying about one-fifth of 
the whole column. 
When only 1 drop of tartaric acid is added, the darkening is not 
quite so distinct, but the precipitate is even more marked, both in 
volume and density. 
Citric acid used instead of tartaric acid gives much the same 
reactions, and the precipitate occupies about one-fourth of the 
whole column. 
Three drops of hydrochloric acid added to the biniodide solution 
produces a yellow tinge, and on the addition of blood the changes 
are much the same as with tartaric and citric acids. The hsemo- 
globin is reduced, the fluid becomes black, and has a peculiar opacity 
characteristic of the presence of all of these acids in the mixture of 
blood and antiseptic. There is a deposit at the bottom of the jar, 
which occuj^ies about one-fourth of the whole column. The fluid 
looks like muddy-brown vinegar. 
If a couple of drops of ammonia be added, the effect is much the 
same as if a similar quantity of caustic potash had been used ; the 
