174 Note on Chemical Analysis by Spectrum-observations, 



n One-tenth of a grain of common salt, carefully weighed in a 

 balance indicating T Apth °f a g ram > was dissolved in 5000 grains 

 of distilled water. Two perfectly similar slips of platinum-foil 

 were then carefully ignited by the Bunsen lamp until they ceased 

 to tinge the flame with yellow light; for to obtain the total 

 absence of yellow light is apparently impossible. One of the 

 slips was dipped into the solution of salt, and the other into di- 

 stilled water, the quantity of the solution adhering to the slip 

 being considerably less than ^th of a grain, and both slips were 

 held over the lamp until the water had evaporated. They were 

 then simultaneously introduced into opposite sides of the flame, 

 when the slip which had been dipped into the solution of salt 

 invariably communicated, to a considerable portion of the flame, 

 a bright yellow light, easily distinguishable from that caused by 

 the slip which had been dipped into pure water. It is thus 

 proved that a portion of chloride of sodium weighing less than 

 t poo 000 th of a grain, is able to tinge a flame with bright yellow 

 light ; and as the equivalent weights of sodium and chlorine are 

 23 and 35*5, it follows that a quantity of sodium not exceeding 

 a boo ooo * n °f a ^ ro y gr am renders its presence in aflame sensible. 

 If it were possible to obtain a flame free from yellow light, in- 

 dependently of that caused by the salt introduced in the experi- 

 ment, it is obvious that a greatly more minute portion of sodium 

 could be shown to alter appreciably the colour of the flame. It 

 therefore follows that much caution is necessary in referring the 

 phenomena of the spectrum of a flame to the chemical constitu- 

 tion of the body undergoing combustion. For the brightest line 

 in the spectrum of the flame of a candle — the yellow line K of 

 Fraunhofer — can be produced in great brilliancy by placing an 

 excessively small portion of salt in a flame, in whose spectrum 

 that line is faint or altogether absent. The question then arises 

 whether this line in the candle flame is due to the combustion 

 of the carbon and hydrogen of which tallow is chiefly composed, 

 or is caused by the minute traces of chloride of sodium contained 

 in most animal matter. When indeed we consider the almost 

 universal diffusion of the salts of sodium, and the remarkable 

 energy with which they produce yellow light, it seems highly 

 probable that the yellow line R which appears in the spectra of 

 almost all flames is in every case due to the presence of minute 

 quantities of sodium. The view which would attribute a great 

 portion of the light of the envelopes of flames to the adventitious 

 presence of minute traces of foreign matter, may possibly serve 

 to explain certain anomalous diversities of colour which arc ob- 

 served in the envelopes of flames arising from the combustion of 

 the 8ame elements. Thus tallow, coal-gas, anhydrous alcohol, 



