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This colour of very del wine belongs to my group C, and 
is not changed by adding sulphite of soda to an acid solu- 
tion ; whereas, as already mentioned, the characteristic colour 
of very new wine belongs to my group B, and if it could be 
obtained in a pure state, would probably become nearly 
colourless on the addition of the sulphite. This difference 
between the colour of new and old wine has enabled me to 
contrive a method by means of which I can ascertain the 
approximate age of port wine kept in the cask. In these 
experiments I have been very much assisted by my friends, 
Mr. Joseph Prestwich, F.R.S., and Mr. Alexander Hay, of 
Sheffield, who have most kindly supplied me with the 
requisite samples. 
On the Age of Dark Wines. 
In order to obtain good results considerable care is required, 
and after trying several methods I found the most satisfac- 
tory was as follows : — I have two experiment cells one inch 
long, made from stout tube, having an internal diameter of 
about a quarter of an inch. Both ends are cut square, and 
one is fastened to a piece of glass like a microscopical object 
by r means of purified gutta perclia. This I find a most 
valuable cement for such purposes, since it resists the action 
of alcohol, acids, and alkalis. The glass must be heated until 
the gutta percha is sufficiently soft. One of the tubes is care- 
fully graduated into ten equal parts, and the other left plain. 
Wine in its natural state is often much too dark coloured to 
enable us to recognise the effect produced by adding sulphite 
of soda, when we examine the spectrum of the thickness of 
one inch. It is, therefore, requisite to dilute it with so much 
of a mixture of one part of alcohol with three of water that 
the spectrum of the light which has passed through the expe- 
riment cells may show a strong, but by no means complete 
absorption of the light in the yellow and in the yellow end of 
the green. After diluting some of the wine to this extent, 
and adding so much citric acid that it may have a very strong 
acid reaction, it should be poured into two test tubes, powdered 
sulphite of soda dissolved in one, and the other kept without. 
Though the sulphite may produce a very considerable change 
at once, the alteration is not complete for a while, and there- 
fore it is best to keep the solutions for an hour or two in the 
tubes, corked up to prevent evaporation. The point to be 
then determined is, how much less thickness of the diluted 
wine to which no sulphite has been added will give exactly 
the same intensity of absorption in the yellow, and in the 
yellow end of the green, as the thickness of one inch of the 
