622 BUNSEN MEMORIAL LECTURE. 



stars, and then of his own applictitioii <^f the principles of spectrum 

 analysis to the examination of terrestrial matter. 



In a letter to mj^self (facsimile, Pis. II-VII), dated November 15, 

 1859, he writes: 



"At the moment I am engaoed in a research with Kirchhotf which 

 gives us sleepless nights. Kirchhoti' has made a most beautiful and 

 most unexpected discovery; he has found out the cause of the dark 

 lines in the solar spectrum, and has been al>le ))oth to strengthen these 

 lines artificially in the solar spectrum and to cause their appearance 

 in a contimious spectrum of a tlame. their positions being identical 

 with those of the Fraunhofer lines. Thus the way is pointed out by 

 which the material composition of the sun and fixed stars can be 

 asiertained with the same degree of certainty as we can ascertain by 

 means of our reagents the presence of SO., and CI. By this method, 

 too. the comi)osition of terrestrial matter can be ascertained and the 

 comj)()nent |)arts distinguished with as great ease and delicacy as is 

 the case with the matter contained in the sun. Thus 1 have been al)le 

 to detect lithium in :^»> grams of sea water. For the detection of 

 many sul)stances this method is to be preferred to any of our pre- 

 viously known processes. Thus, if you nave a mixture of Li, Ka, Na, 

 Ba, 8r, Ca, all you need to do is to l)ring a milligram of the mixture 

 in our apparatus in order to be able to ascertain the presence of all the 

 al)()vc sul)stances ]>y meiv ol)servation. Some of these reactions are 

 wonderfully delicate. Thus it is possible to detect live one-thousandths 

 of a milligram of litiiium with the greatest ease and certainty, and I 

 ha\e discovered the presence of this metal in almost ever}' sample of 

 potashes. " 



The following letter contains the tirst amiouncement of his discovery 



of ctesium. It was not until one month later (May 1(>, 1860) that the 



fact of the discovery was comiimnicated to the Berlin Academy of 



Sciences: 



•■' Heidelberg, April 10, 1860. 



"" ]SIy Dear Friend: AVeltzien went to Paris a week ago and pressed 

 me to accompany him. but unfortunately I was unable to free myself 

 from work which I had postponed until the vacation, and so I have 

 l)een obliged to forego the pleasure of seeing 3'ou in Paris and to tell 

 you how luuch 1 have l)een pleased with your investigation. Do not 

 be annoyed with me. dear Koscoe. that 1 have done nothing with our 

 light investigation. 1 have left everything untouched, because 1 have 

 ol)tained full certainty, by means of spectrum analysis, that l)esides 

 Ka, Na. and Li. a fourth alkali metal must exist, and all my time has 

 been occupied in endeavoring to isolate some compounds of the new 

 suV)stance. Where the presence of this body is indicated it occurs in 

 such minute ([uantity that I almost give up hope of isolating it unless, 

 indeed. I am fortunate enough to tind a material which contains it in 

 larger amount." 



On November 6, 1860, Bunsen describes to me his further work on 

 the new metal as follows: 



"I have been very fortunate with my new metal. I have got 50 

 grams of the nearly chemically pure chloro-platinic compound. It 

 is true that this 50 grams has lieen obtained from no less than 40 tons 

 of the mineral water, from which 2.5 pounds of lithium carbonate 



