328 Mr. R. Cartiuell on a Photochemical Method of 



arranged with their centres in a circle, the figures are extremely 

 beautiful. A pair of elliptic or hyperbolic bands give concentric, 

 elliptic, or hypei'bolic bands of similar or conjugate form crossed 

 by dark bands. 



A series of equilateral triangles gives a six-rayed star, each 

 ray consisting of a multitude of coloured spectra separated by 

 dark bands coiTesponding to the arrangement. In the case of the 

 arrangement, fig. 167 of Sir John Herschel's treatise, I did not 

 obtain the result in fig. 168, but that which I have described above. 



These are a few of the appearances which I have produced, 

 and which may be multiplied to any extent. Beside the appear- 

 ances when the telescope is in focus, which alone have been 

 referred to above, the appearances out of focus are often very 

 remarkable, and in many cases might suggest to the artist de- 

 signs which, both by the symmetry of their forms and by the 

 beautiful arrangement of colours, would perhaps surpass any 

 produced by unaided ingenuity. 



In conclusion, I may mention that Messrs. Elliott, 30 Strand, will 

 supply the apparatus necessary for exhibiting these phsenomena. 



59 Stanhope Street, Hampstead Road, 

 October 7, 1858. 



XXXVI. On a Photochemical Method of recognizing the Non-vola- 

 tile Alkalies and Alkaline Earths. By R. Cartmell, Esq.^ 



AS has long been known, the non-volatile alkalies, when put 

 into the flame of a burning body, have the property of 

 communicating to it peculiar colours ; and in the case of soda 

 and lithia, these colours are of considerable intensity. As a 

 mere trace of soda, however, is sufficient entirely to obscure the 

 colours communicated to the flame by potash or lithia, this as a 

 means of distinguishing between them has hitherto been of very 

 limited application. The following way of detecting them in 

 the presence of each other depends on a means of observing by 

 coloured media the characteristic rays of light which each emits 

 when heated strongly in a colourless gas flame. On account of 

 the homogeneous nature of the colour given to the flame by soda, 

 I thought it possible to eliminate the soda reaction by the use 

 of a coloured medium. After a great many experiments with 

 various coloured solutions and other coloured media, I found 

 that a bluish-coloured solution would best accomplish this object. 

 The only solution that I have yet found to answer perfectly for 

 obliterating the colour of soda, and allowing other rays, namely 

 red ones from lithia and potash, to pass freely through it, is so- 

 lution of indigo. This solution possesses these advantages, — 



* Communicated by the Author. 



