ON EMULSIONS. 
197 
showed, that in the former, the oil was suspended in the form of globules, the 
water occupying the interspaces ; and, in the latter case, the water was globular, 
the oil of course occupying the interspaces. As in the ordinary cases of emul¬ 
sion, the oil is globular, we will, for convenience, call this condition of positive 
emulsion (-)-), and when the water is globular, name it a negative emulsion (—). 
hrom one or two observations, (-f-) emulsions mix freely with water, but not 
with oil, that is, if poured into it, they settle to the bottom as a distinct layer, 
while a negative emulsion poured into oil diffuses through it, but poured into 
water refuses to mix ; if agitated with a large bulk of water, it separates into 
globules, but each globule is not a globule of oil, but of (—) emulsion. 
Two drops of *960 ammonia being added to £ oz. of one of these (—) emul¬ 
sions caused speedy separation of great part of the water, the oily portion 
floating like cream on its surface, but did not mix upon agitation ; a further 
addition of ammonia converted the whole into an ordinary emulsion. 
1 have not yet sought for an agent that would convert a (+) emulsion into 
? (~) form, though such will probably be found in some lead compounds, 
judging from a casual observation. The (—) emulsion being so thick, so nearly 
solid, I put some shot into one of them to facilitate the further mixture of water, 
which it did in so marked a manner that I judged it not a purely mechanical 
effect; the more so when I ascertained that fine gravel did not act in a like 
manner, but each little pebble attracted to its surface a film of water. The 
shot did not specially attract either water or oil. 
2 drachms of oil and 4 of water, being converted into a (—) emulsion by 
ten minutes’ agitation with clean shot, showed scarcely any appearance of sepa¬ 
ration after standing at rest for four days. 
Castor oil and almond oil both showed much less willingness to mix with 
water in anything like equal proportions, only a small portion of oil remaining 
suspended in the water, and a small portion of water in the oil. Balsam of 
copaiba very readily yielded a negative emulsion when agitated with successive 
small portions of water till the bulk of water equalled or exceeded that of the 
balsam; it was a thick creamy yellowish semifluid: the addition of a little 
solution of potassa made it much whiter and mobile, by converting it into a posi¬ 
tive emulsion. 
Solution of bicarbonate of magnesia promotes the formation of negative emul¬ 
sion between water and almond oil; solution of diacetate of lead has the same 
effect with water and olive oil; the addition of acetic acid to the latter till 
it had an acid reaction did not alter its character. 
Two or three years ago, while experimenting upon the intersolubility of 
liquids, I observed that strong liq. ammonias, agitated with an equal bulk of 
ether, boils violently. They become viscid and opalescent if agitated in a 
stoppered bottle, and if the stopper be removed while they are mixed the disen¬ 
gagement of gas throws the fluids out of the bottle; but if allowed to separate 
under pressure they are not disturbed by the removal of the stopper. From 
the viscidity of the mixture of two liquids usually so mobile, I conjectured they 
were in the condition of a negative emulsion. 
The relation of emulsibility to intersolubility is a branch of the subject sug¬ 
gestive of interesting speculations. 
There is also an interesting group of questions to be investigated, relating to 
the influence of the relative density of the suspended matter and its medium, 
the state of division to which the former is reduced, and the viscosity or mo¬ 
bility of the latter and their effects upon emulsifaction. That density alone is 
not sufficient to ensure rapid subsidence we have illustrated in the observations 
recorded by Faraday (on gold in relation to light) in which he found gold in a 
tine state of division remained suspended in water for months. 
I have added one or two observations which bear also upon the mobility of 
