1861.] on Bunsen and Khchhoff's Spectrum Observations, 325 



chloride of calcium, chloride of strontium, chloride of barium, 

 containing at most yttJ^^ P^^*- ^^ * grain of each substance. 

 This mixture I put into the flame, and observed the result. First, 

 the intense yellow sodium line appeared, on a background of a pale con- 

 tinuous spectrum ; as this began to be less distinct, the pale potassium 

 lines were seen, and then the red lithium line came out, whilst the 

 barium lines appeared in all their vividness. The sodium, lithium, 

 potassium, and barium salts were now almost all volatalized, and after 

 a few moments the strontium and calcium lines came out, as from 

 a dissolving view, gradually attaining their characteristic brightness 

 and form." 



We can thus detect the most minute traces of any one of these 

 bodies, if mixed with the largest quantities of any other substance. 

 The delicacy and accuracy of these reactions is without parallel, as is 

 seen from the following statements :— 



1. Soda 3,000,000 part of a milligramme, or ibo.ooo,ooo part of a grain of 

 soda can be detected^ Soda is always present in the air. All bodies 

 exposed to air show the yellow sodium line. If a book be dusted neiir 

 the flame the soda light can be seen. 



2. Lithia jod'ooo P^rt of a milligramme, or eo^ooo.ooo P^rt of a grain of 

 lithia can easily be detected. Lithium was only known to occur in 

 four minerals. It is now found by spectrum analysis to be one of the 

 most widely distributed elements. It exists in almost all rocks ; it has 

 been found in 3 cubic inches of sea, river, and Thames water ; in the 

 ashes of tobacco, and most plants ; in milk, human blood, and mus- 

 cular tissue. * 



3. Strontia foo^ of a milligramme, or 1,000,000 parts of a grain of 

 strontia can easily be detected. 



4. Lime loojooo o^ ^ milligramme, or fjooboo of a grain may be easily 

 detected. 



In examining the spectra of the alkalies obtained from certain 

 mineral waters, Bunsen observed the occurrence of two bright blue 

 lines which he had not seen before, when he examined alkalies from 

 other sources. Hence he concluded that these bright lines must be 

 produced by a new, hitherto undetected, alkaline metal. Subsequent 

 search proved the validity of the supposition. The new metal was 

 found and isolated. The analogy between this discovery and a cele- 

 brated one in another branch of physical science, will be at once 

 understood. As Adams and Leverrier discovered Neptune, so 

 Bunsen discovered " Ccesium " by the perturbations produced in the 

 spectra of the other alkaline metals. 



This is, however, not all. A few days ago the speaker received a 

 letter from Bunsen, which contains the following most interesting infor- 

 mation : — " The substance which I sent you as impure tartrate of 

 Caesium contains a second new alkaline metal. I am at present engaged 

 in preparing its compounds. I hope soon to be able to give you more 

 Vol. III. (No 33.) . z 



