440 Mr. H. C. Sorby on Analysis of Animal and Vegetable [Apr. 11, 



when redissolved in water and filtered to remove anything not soluble 

 in that liquid. This clear solution should then be evaporated to dryness 

 at a gentle heat in a small saucer, and kept dry ; for then the colours often 

 undergo no important change in the course of many months, whereas, when 

 kept dissolved in water or alcohol, they may quickly decompose. I have 

 thus prepared the colouring-matter of above a hundred different vegetable 

 substances, some of which have become entirely changed, but a large 

 number are apparently still unaltered. I have also kept a number of 

 colours, sealed up in glass tubes, ready for direct examination, dissolved 

 in alcohol, in strong syrup, or in alum. Many have decomposed, but 

 many have kept perfectly well, or have merely faded, and still give excel- 

 lent spectra after above a year. I have also prepared and kept in the 

 same manner some animal colouring-matters, but comparatively few. 



8. Method of examination. 



The coloured substances are examined, when dissolved in water, alcohol, 

 or other solvent, in the small glass cells already described, and the various 

 reagents are added and mixed by means of a moderately stout platinum 

 wire, flattened at one end and turned up square, like a little hoe. I have 

 made many experiments in order to ascertain what reagents are most ser- 

 viceable in developing characteristic spectra, and have at length concluded 

 that for general purposes the following are the most convenient. Those 

 which are solid are best kept in small bottles as coarse powder, and added 

 to the small cells in a solid state, so that the quantity used may be more 

 readily known. 



9. Reagents. 



Hydrochloric acid. 



Citric acid. 



Benzoic acid. 



Boracic acid. 



Bicarbonate of ammonia. 



Carbonate of soda. 



Diluted solution of ammonia. 



Caustic potash. 



Sulphite of soda. 



Sulphate of protoxide of iron. 



Alum. 



Iodine dissolved in alcohol. 

 Bromine dissolved in water. 

 Solution of hypochlorite of soda. 

 Permanganate of potash. 



This list might of course be very much extended, if we were to include 

 such reagents as may be used in separating or decomposing colours by the 

 ordinary chemical methods. In describing the effect of those named in 



