188 
POPULAR SCIENCE REVIEW. 
in from seven to fifteen minutes if to each litre there be added -04 
grammes of finely-povrdered alum, care being taken to agitate the liquid 
■when the alum is introduced (this is about fib /per ton of water). If potash 
alum is used, the alum is decomposed into sulphate of potash (which is all 
dissolved by the water) and sulphate of alumina, which, by its decomposi- 
tion, purifies the water. The alumina separates in an insoluble form, and 
carries down with it, as it precipitates, the matters which render the water 
turbid, and the organic matter. The acid attacks the alkaline and earthy 
carbonates, and transforms* them into sulphates. The water becomes slightly 
richer in bicarbonates and free carbonic acid, whilst all organic matter is 
destroyed. Seven parts of sulphate of alumina will purify as much water as 
ten parts of rock alum or potash alum, and the sulphate of alumina does not 
introduce any alkaline sulphate into the clarified water. 
Antidote to Phos}ihorus. — It is asserted by a writer in one of the late num- 
bers of the Bulletin de Therapeutique that turpentine is a very useful antidote 
in cases of phosphorus poisoning. What is the explanation of this quality ? 
The Determination of Nitrous Acid. — In a paper recently laid before the 
Fi’ench Academy, M. Chabrier, who has been studying the difierent oxides 
of nitrogen, gives these two conclusions: — (1) in liquids containing at 
the same time nitrites, nitrates, and organic matter, the nitrous acid of the 
nitrites may be determined by the decolorising action which hyposulphite 
of soda exerts on the iodide of starch, produced by the reaction of the 
nitrites on iodide of potassium, in presence of starch and dilute sulphuric 
acid ; (2) in the absence of nitrates and organic matter the determination 
can be more easily made by the decoloration of indigo solution, operating 
with the aid of heat, but out of contact with the air. 
The Purijicaticm of Metallic Bisinuth. — In the Pharmaceutical Journal for 
January, Mr. C. II. Wood states that the officinal process for the purification 
of bismuth is in accordance with the method indicated by most chemical 
authorities. Gmelin, Watts, and other authors state that the impurities of 
bismuth are removed by fusion with nitre. Schacht’s experiments suffi- 
ciently demonstrate the possibility of removing the whole of the arsenic by 
this means. It is true, says Mr. Wood, that, in some fusions, Schacht found 
a portion of the arsenic still remained in the metal j but we are not informed 
what the proportions were before and after, and we have every right to 
assume that, by continuing or repeating the process, the whole might have 
been removed in these as in the other cases. Ilis own experiments have 
sufficiently satisfied him that the Pharmacopoeia method is an efficient one 
for the complete removal of arsenic, antimony, and sulphur. The most 
careful application of Marsh’s test lias failed to detect either of the former 
substances in any sample of the metal he has purified. 
The Preparation of Cerium. — A note in the Scientific American for Feb- 
ruary gives the following a.s the mode of preparing this metal adopted by 
Wohler: — A solution of the oxide in hydrochloric acid is mixed with equal 
parts of chloride of potassium and chloride of ammonium, and evaporated to 
dryness, fused, and poured out to partially cool, and then coarsely pulverised 
and mixed while still warm with pieces of sodium, and the whole projected 
into a clay crucible previously heated to redness. In this manner the 
cerium is reduced, and appears in the slag in the form of two pellets, which 
can be collected and fused into one mass. 
