426 
POPULAR SCIENCE REYIEW. 
to the manufacturer. The following method, which has been given by Herr 
Engelhardt in Dingier' s Polytechnisches Journal, is therefore of interest; — A 
given quantity of palm oil is placed in an iron pot, heated to about 62° C., and 
allowed to stand all night. The next day it is poured into a clean vessel and 
cooled to 40° or 87° 0. Meanwhile a certain quantity of water, say for 
instance 45 kilogrammes of water to 1,000 of palm oil, is set to boil ; in it 
are dissolved 15 kilogrammes of bichromate of potash, and when the solu- 
tion has cooled a little, 60 kilogrammes of chlorhydric acid are added. This 
mixture is then poured into the palm oil, which must be quickly stirred, 
and in about five minutes it will assume a sombre green colour from the re- 
ducing action of the combination of the chromate with the chlorhydric acid. 
By continuing to stir, the separation of the oxide of chromium is completed, 
and the oil gradually clarifies and becomes at last quite limpid. In order to 
render it quite white it is now only necessary to wash it in warm water ; 
if, however, it should not appear quite colourless, the operation must be 
repeated with 0"25 kilogrammes of red chromate and 1 kilogramme of 
chlorhydric acid. This method is quick, free from danger, and produces 
very good results. The author declares that the new methods in which 
either gaseous chlorine, chloride of lime, or a mixture of chlorhydric acid 
with peroxide of manganese are proposed, are much inferior to the above 
process. 
S^ome Experiments on chemical Filters. — In a paper published in a recent 
number of the American Journal of Pharmacy, Mr. Charles E. Avery 
records some very interesting experiments which he conducted on filters, in 
order to determine how to obtain the gTeatest rapidity of efficient filtration. 
We give his own words. After describing some preliminary observations, 
he says, ‘^it occurred to me to fold the plain qualitative filter in two 
operations instead of one. In place of folding the filter doubled upon itself 
down the middle in the usual way, I proposed to turn down on each side of 
the paper a fold equal to one- quarter of the semicircle, and then to fold 
the sections of 45° arc thus formed back upon themselves. The filter is 
then opened without disturbing the folded portions, and placed upon the 
funnel. In this form the triple side of the plain filter is broken up, and 
the folded portions keep open passages, instead of hindering filtration. 
This filter, as tried against the plain form, gave, 1st, 138 : 100. 2nd, 111 
+ : 100. 3rd, 205 -f : 100. Two plain filters ran equally in several trials j 
each was changed into the other’s funnel, and No. 1 ran 33 per cent, less 
than No. 2. No. 1 was dried and folded into my form ; remaining in the 
same funnel, it ran 32 per cent, faster than the other. Both filters were 
then opened, and showed no tear or weakness when held against the light. 
As these filters gave different results in different funnels, I thought I would 
ascertain the cause. The water seemed to be retarded in its passage by the 
attraction of the glass ; therefore, those funnels having the greater portion 
of the paper free from the glass would be the best j that is, a hroad-throated 
funnel, other things being equal, will filter faster than a narrow-throated funnel. 
To test this point I selected two large funnels ; No. 1 had three times as 
broad a throat as No. 2. With the first filters they ran, 117 : 100. 123 : 100. 
133 : 100. 118 : 100. The reason for this low difference was found in a 
thin spot near the point of No, 2. Other sets of filters gave — 2nd set, 
