330 Mr. K. Cartmell on a Photochemical Method of 



The indigo solution is conveniently made by adding water to 

 the common indigotic acid of the laboratories till the point is all 

 but reached where an intense flame of soda appears slightly 

 pink when observed through the bottle (of the size and shape of 

 a common watch) filled with the solution. 



The blue glass hitherto used is very thick and of considerable 

 depth of colour; but on repeating these experiments, I have 

 found that the blue glass as usually obtained from the manufac- 

 tory, when increased to the same depth of colour by putting two 

 pieces together, answers the purpose perfectly. Before using 

 these glasses, it must first of course be ascertained how small a 

 quantity of potash mixed with soda or lithia they will clearly 

 indicate. 



For the success of these experiments the importance of em- 

 ploying a perfectly colourless flame is obvious. I have used the 

 flame of a Bunsen's lamp, which is of the palest blue except 

 just at the tip, and devoid of any trace of red. The most intense 

 flame of soda should only make this blue a little brighter when 

 viewed through the indigo solution. 



The substances to be exposed to the flame are conveniently 

 supported on the finest platinum wire 

 melted on to a glass stand, and the /^ 



wire is to be somewhat curved, as in (^ 

 the subjoined diagram. The curved ~ 

 part is first heated, and so introduced 

 into the flame that the point of the wire 

 where the substance rests is just within 

 the edge of it. "NMien the wire is some- 

 what curved and heated as above di- 

 rected, it hinders the escape of the sub- 

 stance from its proper position. 



The alkalies are best tested for in the state of sulphates, as 

 these salts do not volatilize so rapidly as the chlorides, and hence 

 their colours are more permanent. To increase the intensity of 

 these reactions, it is only necessary, after having put the sub- 

 stance contained on the point of the wire into the reducing flame, 

 to moisten it with hydrochloric acid and to hold it again in the 

 edge of the flame. 



In making these observations, care should be taken not to 

 mistake the glowing platinum wire for a coloration of the flame. 

 The coloured rays passing immediately upwards from it are only 

 to be regarded. 



Separation of the Alkaline Earths. 

 Hitherto, in the detection of strontia by means of the colour 

 communicated by its chloride to the flame of alcohol, there has 



