336 Aprunny—Photographs of Spark Spectra from the Rowland Spectrometer. 
The manganese spectrum by sparking a saturated solution of potassium 
permanganate in a similar manner. 
The electrodes used with such solutions were made of six plates of ordinary 
stout platinum foil, placed close together and fused into one end of a glass tube. 
The glass tube containing the solution and carrying the lower electrode was of a 
U shape, the open end being prolonged sufficiently above the closed end, to act 
as a reservoir for the liquid, and to exert a slight pressure upon the electrode so 
as to keep it fed continuously. ‘The glass tube carrying the upper electrode was 
straight, and was also filled with the solution. With a little experience, electrodes 
of this form may be made to feed solutions of different strengths perfectly. 
The advantage of platinum electrodes over pure graphite ones lies in the fact 
that during the necessarily long exposures they do not become shorter by combustion 
or disintegration of the material. 
The specimen of gold was obtained from crystallized gold chloride, by preci- 
pitation with pure oxalic acid, washing and redissolving in aqua regia, and again 
precipitating with oxalic acid. The precipitated gold was finally fused under 
borax in a clay crucible. 
The original photographs were taken from the first order of spectra; and the 
reproductions published with this communication are of the same size as the 
originals. The definition of the lines of this order is extremely fine, and the 
dispersion quite sufficient for most practical purposes. For these reasons it has 
been deemed inexpedient to have enlarged reproductions prepared for publication. 
A further most important feature of this order is that the lines are the least 
distorted by the astigmatism of the grating, so little indeed that the characteristics 
of the component lines are quite apparent from the photographs, and the general 
character of the spectra are wholly unaffected. By the characteristics of the com- 
ponent lines is meant their peculiar features as observed in prism spectra, that is 
to say, whether extended or not, continuous or discontinuous, well defined or 
nebulous. 
On comparing these photographs with those obtained by Eder and Valenta, 
and also with those of Exner and Haschek, important differences are to be 
observed; many lines photographed by those observers are absent ; differences are 
also occasionally observable in the character of the lines. 
Some of these differences are possibly due to a greater degree of purity in the 
elements and compounds examined, but the majority, however, are certainly to be 
ascribed to the different methods of sparking employed by the several observers. 
Attention may be drawn to the marked effect which the sparking of the 
solutions of potassium chromate and permanganate between platinum electrodes 
has upon the character of some of the lines of platinum. 
Careful measurements of the wave-lengths of the lines in the photographed 
