114 REPORTS ON THE STATE OF SCIENCE.—1918. 
(3) Drop Method. The principle involved is that one can dilute 
an emulsion by adding more of the continuous medium. (See 
Newman, Journ. Phys. Chem., 18, 34-55 (1914). ) 
Now these methods are not suitable for a solid emulsion such as 
margarine, though the staining with dyes, followed by an exami- 
nation of a thin film under the microscope, sometimes gives valuable 
indications. The electrical :onductance of margarine, the heat con- 
ductance, and the viscosity would seem to offer suitable lines of re- 
search in this problem of distinguishing the nature of the phases. 
If the margarine were an. oil-in-water emulsion, one would 
anticipate a possible electrical conductance (since there is at least 
1 per cent. NaCl present), on the same lines as the conductivity 
through a set jelly, e.g., gelatine. But with a water-in-oil emulsion, 
the conductivity (if any) would be very small indeed, inasmuch as 
the contiguous particles are now fat, whieh is characterized by its 
insulating properties. 
Again, it would be most interesting to investigate the heat con- 
ductivity of two solid emulsions having inverted phases. The 
corresponding case of the heat conductivity of a set jelly still remains 
for research. 
Possibly information would be afforded by the viscosity of a solid 
emulsion. The réle ef viscosity in colloid researches is increasingly 
manifested, and “the great importance of viscosity measurements as 
the most delicate means of tracing slight changes in colloidal solu- 
tions is fully recognized’ (HK. Hatschek). Indeed, with an emulsion 
like margarine, with an average ratic of oil to water, 3°6 :1, one would 
anticipate notable variations in viscosity depending on whether the 
oils and fats constituted the disperse or continuous medium. 
There are many other problems of a colloid nature connected with 
margarine, but they are only apparent to one actually in contact with 
the entire process. Thus, why does soured milk yield a better 
emulsion with the oils and fats than sweet milk? Certainly, no 
very sound theory is as yet proposed, though it is interesting to note 
that oils and fats containing a small percentage of free fatty acids 
will mnch more easily emulsify with water than will neutral oils 
or fats. Since sour milk is distinctly acid (lactic acid), there would 
seem to be some connection here, but mineral acids cause emulsions 
to “ break.” 
Finally, in connection with margarine manufacture, one research 
of great importance is suggested by the use of the various emulsify- 
‘ing agents previously referred to. So far, little work has been 
published describing what one may term the ‘ emulsifying efficiency’ 
of such an agent. Thus, to make a concentrated stable emulsion of 
an oil in water, one adds gelatine, starch, gum, flour, etc. It would 
be very interesting to arrange these substances in the order of their 
capacity or power of stabilising a standard-strength emulsion, and 
then investigating the possible counection between the “ emulsifying 
efficiency ” and the gold number, viscosity, surface tension, etc., of 
their pure solutions in water (cf. Moore & Krombholz, Brit. Journ. 
Physiol. 22, 54 (1908) ). 
