1873.] Spectroscopic Quantitative Analysis of Alloys. 507 



crystallize on a slip of glass, and crystals small enough to be transparent 

 were examined by daylight with an g-inch objective; no remarkable dif- 

 ference was observed in the colour of different crystals of the same thick- 

 ness, and the polariscope did not show them to be pleochroic, the two 

 contrasting colours, violet and red, being due to different thicknesses 

 of crystals. To aid me in the above experiments, Messrs. Howards 

 and Sons, of Stratford, very generously supplied me with the sulphates of 

 cinchonidine and quinidine in a pure state ; and I beg to offer them my 

 best thanks for the kindness. The iodine compound of the tetrethyl- 

 ammonium occurs in prismatic crystals resembling the sulphate of iodo- 

 quinidine, but exhibits no property of interest. 



II. <{ On the Quantitative Analysis of certain Alloys by means 

 of the Spectroscope/'' By J. Norman Lockyer, F.R.S., 

 and William Chandler Roberts, Chemist of the Mint. 

 Received November 20, 1873. 



(Abstract.) 



The authors, after referring to experiments which showed clearly that the 

 spectroscope might be employed to detect minute differences in the com- 

 position of certain alloys, proceed to give an account of the researches 

 which they had instituted with a view to ascertain the degree of accuracy 

 of which the method is capable. 



The image of an electric spark passing between the unknown alloy 

 and a fixed electrode being thrown by means of a lens on the slit 

 of the spectroscope, the phenomena observed were found to vary with 

 the composition of the alloys ; and further, by arranging them together 

 with known check-pieces on a suitable stand, and bringing them in turn 

 under the fixed electrode, the composition of the unknown alloys was de- 

 termined by comparison with the known check-pieces. 



The shape of the electrode ultimately adopted was that represented 

 in the sketch ; and these pieces were held in their places 

 by suitable metallic clips. Special attention was then 

 directed to the adjustment of the length of the spark, 

 which was found to materially influence the phenomena. 

 The method adopted consisted in placing the variable 

 electrode in the field of a fixed microscope having a 

 3- or 4-inch objective, and adjusting the summit of this electrode 

 coincide with the spider-lines of the eyepiece. 



After a series of experiments on alloys of zinc and cadmium of various 

 compositions, the results of which were shown on a curve, more extended 

 trials were made with the gold-copper alloy employed in coinage, which 

 was peculiarly suited to these researches in consequence of the known 

 method of assay having been brought to so high a state of perfection (the 

 composition being determined with accuracy to the ^ part of the original 

 assay-piece of about 7 grains), and from the fact 'that reliance can be 



