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These "doubtful" samples, which contain approximately 8-5 per cent, of solidsnot-fat,
are generally found to give other analytical criteria approximately
coinciding with the lowest figures given by genuine milk; they receive the most
elaborate analysis, but, individually, they usually have to be reported as
"genuine" or "possibly genuine," owing to the difficulty of proving the
addition of a small percentage of water to an article which itself contains about
88 per cent, of water and which is subject to natural variations in its composition.
Collectively, however, their effect although slight, becomes significant.
Hot Milk.—Nine samples of hot milk were taken from various cafes in the
Borough during the year, one of which was found to contain 6 per cent, of added
water. The remainder were genuine and of good quality.
Canned Sild : Tin.—Following the analysis of a sample can of Sild (small
herrings caught chiefly off the coast of Norway) which showed contamination
by tin to the extent of 2.7 grains per pound, nine further samples were taken
from different boxes of the same consignment.
Of these samples, six were found to be contaminated with tin, in amounts
varying from 2.2 to 4.6 grains per pound, and the other three were passed, as
they contained less than 2 grains of tin per pound.
While it is obviously undesirable that there should be any metallic contamination
of food, it is necessary for practical administrative purposes to adopt a
certain fixed limit as the standard, above which the food must be rejected;
and in the absence of any legal standard, the limit of 2 grains of tin per pound
as a quantity "potentially injurious to health," which was recommended by
the Local Government Board Report in 1908, has been generally accepted and
applied.
The consignment of the brand of sild referred to was, unfortunately, a large
one, comprising 20 boxes of 100 tins each, in all 2,000 tins of sild, and in order
to avoid destroying boxes which might have been quite satisfactory, samples were
then taken from every box; where the results on these samples were near to the
standard mentioned, further samples were taken from the same boxes. In all,
43 "follow-up" samples were taken, of which 23 contained tin in excess of 2
grains per pound. The boxes yielding the excessive proportions of tin contamination
were surrendered by the dealer and their contents destroyed, while the
remainder were passed on the condition that any tins not sold within a very
short period should be destroyed, since the proportion of tin tends to increase
on storing.
Unfortunately the determination of tin is a lengthy process, involving the
digestion of portions of the sample in boiling nitric and sulphuric acids for
several hours, followed by precipitation of the tin by sulphuretted hydrogen, and
considerable difficulty was experienced in carrying out so many tin determinations,
in duplicate, in the poisonous atmosphere created.