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same acted on by the sulphite of soda. The uu graduated tube 
should, therefore, be filled with the latter, and a small piece 
of thin glass placed on the top, so that the light may pass 
through exactly one inch in thickness of the liquid, and none 
run out when the tube is placed in an inclined position on 
the side stage of the spectrum eye-piece. The diluted wine 
should then be introduced into the graduated tube, which is 
placed nearly vertically on the ordinary stage of the micro- 
scope, and the depth of the liquid carefully regulated by means 
of a pipette, so that the intensity of the absorption in the two 
spectra may be exactly the same in the yellow and in the 
yellow end of the green. The light must be of the same 
intensity in both spectra, and therefore it is also particu- 
larly necessary so to regulate the instrument that the trans- 
mitted red rays may be of exactly the same brilliancy. The 
accuracy of this experiment is limited by the difficulty of 
recognising when the transmitted and the absorbed rays are 
equal in both spectra, and by its being difficult to determine 
the depth of the diluted wine to less than of an inch. 
The actual value of the measurements varies to some extent, 
according to the manner in which the experiments are made, 
and therefore I strongly advise any one who may wish to 
employ this method to prepare for himself a table of the com- 
parative amount of change of wines of various ages. 
When sulphite of soda is added to a faded solution of the 
colouring matter of fresh dark grapes it is changed to a pale 
orange yellow, which colour is, I believe, due in great measure 
to the presence of the same yellow substance as is met with 
in green grapes, so that the intensity of absorption is reduced 
to about -po, or from l'OO to TO. In the case of the perfectly 
new wine prepared by myself, the intensity of absorption was 
reduced from l’OO to about ‘ 22 . My experiments with the 
wines of commerce were chiefly made in April, 1868. The 
newest port wine that I was able to examine was of the vintage 
of 1866, and therefore about one year and a half old, and 
even this contained a good deal of the C colour. I examined 
several specimens of the same vintages of various older dates, 
which differed considerably in general colour and character, 
but when all had been kept for the same time in the casks I 
did not find any material difference in the general results. 
From the manner in which the experiments were made, 
the change produced by adding the sulphite of soda is referred 
to the amount of the C colour taken as unity; and, assuming 
that the extent to which the wine has been altered by 
keeping is the difference between the amount still unchanged 
and unity, the numbers given indicate the relative changes 
