CUT} 
non-volatile fatty acids and fatty acids which are volatile with 
water vapour such as butyric acid. This has been the means to 
distinguish the fat of milk from other kinds of fat. 
As it was generally supposed that the amount of volatile fatty 
acids in the fat of cow’s milk does not vary considerably, the deter- 
mination of the amount of volatile fatty acids has been applied as 
a means to detect the adulteration of butter with other kinds of fat 
(margarine) and this is still done at the present time. 
In this investigation a conventional method is usually adopted, which 
does not reveal the total quantity of the volatile fatty acids, but 
gives a number which serves as a measure for the amount of volatile 
fatty acids and at the same time enables us to form an opinion as 
to the genuineness of the butter. 
According to this conventional method 5 grams of filtered butterfat are saponified 
with 2 cc. of very strong soda-lye, with addition of 20 cc. of glycerin. After addition 
of 90 cc. of hot water the soap is decomposed with 50 cc. of dilute sulphuric acid. 
With due regards to certain rules the liquid is distilled until 110 ec. are collected. 
The distillate is titrated, after filtration, withn/,, baryta water (indicator phenolphtha- 
leïne). The number of cc. of baryta water required for the neutralisation, gives the 
figure which represents the amount of volatile fatty acids and is called the Rrrcuerr- 
MetssL-WoLLNy-number, (R.M.W.-number). 
For the examination of milkfat, the determination of the index 
of refraction has come into use of late. It has been ascertained that 
this physical constant is smaller with fat of milk than with nearly 
all other kinds of fat. 
For the determination of the index of refraction of milkfat, the oleorefractometer of 
Zuiss is always used. Instead of the real index of refraction the so-called refraction- 
number is generally given. This is the number of the empirical division of the scale 
of the instrument, which coincides with the line of demarcation. (The refraction-number 
40 corresponds with the index of refraction 1.4524; 60 with 1.4659.) 
It is remarkable, that the butter, which in certain months 
of the year is being produced in the northern provinces of the 
Netherlands, shows a considerable lower K.M.W.-number and a con- 
siderable higher refraction-number than butter, produced in other 
parts of the country in the same season. From an economical, as 
well as from a scientific point of view, it is of importance to trace 
the reason of this. 
With regard to the economical side of the problem, which has 
caused this investigation, it must be mentioned that the butter 
exported from the Netherlands with a low R.M.W.-number and a 
high refraction-number, has, in other countries, been repeatedly charged 
with containing foreign fat. Latterly it has become known that the 
fat of our milk possesses an abnormal composition during certain 
