434 
POPULAR SCIENCE REVIEW. 
Improvements in Chlorimetry. — Mr, J. Smith, M.A., read a paper before 
the British Association at Edinburgh on Improvements in Chlorimetry.’^ 
He showed that the use of the milky solution of bleaching powder in chlori- 
metry is unsatisfactory, and hence it was necessary to discover a method of 
securing a clear solution containing all the chlorine by dissolving it in an 
alkaline solution. This is conveniently done by adding, say, ten grammes 
of bleaching powder to twenty grammes of soda crystals, filtering out the 
precipitated carbonate of lime, which is known to be washed, when it no 
longer discharges the colour of dilute sulphate of indigo, and making up the 
filtrate by water to one like of fiuid. It is a clear colourless liquid of the 
specific gravity of 1*007, but if made of specific gravity 1*233 slightly 
greenish, having a pleasant oily feeling between the fingers, contrasting 
favourably with the roughness of the decanted solution of the bleaching 
powder with which it gives a precipitate. Most satisfactory results are ob- 
tained from it by all the chlorimetrical methods, and it has the additional 
advantage of showing the amount of lime in the sample by adding a solution 
of known strength of carbonate of soda until a precipitate is no longer 
formed. 
Dichroism of the Vapour of Iodine . — Professor Andrews read a paper 
before the British Association on The Dichroism of the Vapour of Iodine.” 
The fine purple colour of the vapour of iodine, he explained, arises from its 
transmitting freely the red and blue rays of the spectrum, while it absorbs 
nearly the whole of the green rays. The transmitted light passes freely 
thi’ough a red copper or a blue cobalt glass. But if the iodine vapour be 
sufficiently dense, the whole of the red rays are absorbed, and the trans- 
mitted rays are of a pure blue colour. They are now freely transmitted as 
before by the cobalt glass, but will not pass through the red glass. A 
solution of iodine in sulphide of carbon exhibits a similar dichroism, and, 
according to its density, appears either purple or blue when white light is 
transmitted through it. The alcoholic solution, on the contrary, is of a red 
colour, and does not exhibit any dichroism. 
The Phosphate Process with Sewage . — Messrs. Forbes and Price described 
their process to the British Association. This process, it was stated, was in 
operation at Tottenham. The sewage, after passing through some depositing 
tanks which had been constructed for the lime process, was pumped up at 
the rate of 800 or 1,000 gallons per minute along a carrier into a tank a 
hundred yards long, and of gradually increasing breadth. This tank took 
three hours to fill. As the sewage passed along the carrier the chemicals 
were mixed with it thus : — Two boxes were placed over the carrier — one a 
few yards further along it than the other ; the first contained the phosphate 
mixture, and the second milk of lime. Men were continually stirring the 
contents of each box, which were allowed to run continuously into the 
sewage as it passed beneath the boxes. The amount of the preparation 
added was not ascertained, but it was stated to be certainly much less than 
the proportion indicated by previous experiments (one ton to 500,000 gallons 
of sewage). 
