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85
It has been stated by the defence that it is a very terrible thing to condemn
a sample of milk owing to a difference of one hundredth of a degree
(equal to 1.9 per cent, of added water). This would be true if an ordinary
household thermometer were used.
The actual thermometer used is about 2 feet in length and there are
only three degrees on the scale, one above zero and two below zero. Each
degree is approximately 4 inches in length and is further sub-divided into
tenths and hundredths. A tenth of a degree is about three-eighths of an inch
in length, and one-hundredth of a degree is about equal to one degree on an
ordinary thermometer.
One hundredth of a degree can, therefore, be read easily by any one with
the naked eye.
Using a magnifier attached to the thermometer, the thermometer can be
read accurately to one-thousandth of a degree (.001° C.) each way, i.e., .527
might be .526 or .528. This difference of .001 would represent 0.2 per cent,
of added water. The apparatus is, therefore, accurate to 0.2 per cent, of
added water.
Accuracy of
thermometer
readings.
Owing to the delicacy of the thermometer it is necessary to check any
inequality of the thread or graduations. This is carried out by means of sugar
solutions of known concentration. The extremes —0.422° C. and —0.621° C.
are first checked. Obviously a slight inaccuracy is not important where the
sample is heavily watered or in the case of genuine samples. The range is
therefore shortened so as to ensure accurate results in cases where the amount
of added water is small and determinations are made at a number of points
within the range —0.487° C. to —0.537° C.
Also, before a sample of milk is tested the zero point is always checked
by determining the freezing point of boiled distilled water.
Standardisation
of the
thermometer.
Many questions are asked with regard to the rate of stirring, tapping
the thermometer, super cooling, etc. It should surely be conceded that a
trained chemist is capable of carrying out the test correctly according to the
directions laid down.
The
Hortvet
technique.
Objections were raised by the defence because the determination of the
freezing point had not been carried out by the public analyst himself. This
involved the appearance of both my assistant and myself to give evidence.
It is obvious that in a busy laboratory it is impossible for the public Analyst
to carry out determinations on all samples which may or may not be genuine.
In Bakewell v. Davis, 1894, where the analysis had been carried out by
an assistant under the supervision of the Public Analyst, the judges were of
opinion that the Public Analyst had analysed the sample within the meaning
of the Act.
Determination
of
Hortvet
figure by
assistant.
When samples do not comply with the Sale of Milk Regulations proceedings
are taken under Section 2 (1) of the Food and Drugs (Adulteration)
Act, 1928, which states that "No person shall sell to the prejudice of the
purchaser any article of food or any drug which is not of the nature or not of
the substance or not of the quality of the article demanded by the purchaser."
With the advent of the Hortvet test proceedings are taken also under
Section 4 (1) of the Milk and Dairies (Amendment) Act, 1922, which states
that "No person shall add any colouring matter or water to milk
intended for sale and no person shall . . . sell, or offer or expose for sale
any milk to which any such addition has been made."
Legal
procedure.