1883.] 



On Radiant Matter Spectroscopy. 



263 



alkaline earths, and alkalies. Ammonia added to this solution would 

 precipitate an earth, and in the filtrate oxalic acid would precipitate 

 an insoluble oxalate, showing the citron band strongly. This was 

 found on analysis to consist of strontic and calcic oxalates. The 

 strontia being separated, the remaining lime formed an oxalate which 

 gave the citron band. 



So far all the chemical evidence went to show that the band- 

 forming substance was calcium, and further tests tried with the 

 purified oxalate confirmed this inference. Every analytical test to 

 which it was subjected showed lime, and nothing but lime ; all the 

 salts which were prepared from it .resembled those of lime, both 

 physically and chemically ; the flame spectrum gave the calcium 

 lines with extraordinary purity and brilliancy ; and, finally, the atomic 

 weight, taken with great care, .came out almost the same as that for 

 calcium, 39*9 as against Ca 40. 



On further examination it was found that most native compounds 

 of lime gave the citron band. It was found in clear and colourless 

 Iceland spar, native calcic phosphate, a crystal of arragonite, a 

 stalactite of calcic carbonate from Gibraltar, cinnamon stone (lime 

 alumina garnet), iron slag from a blast-furnace, pink coral, com- 

 mercial plaster of Paris, and most specimens of ordinary burnt lime. 



Evidence stronger than this in favour of the view that the citron 

 band was an inherent characteristic of calcium could scarcely be ; 

 "but, on the other hand, there was evidence equally conclusive that the 

 band was not essential to calcium. 



Starting with a lime compound which showed the citron band, I 

 could always obtain a calcic oxalate which gave the band stronger 

 than the original substance ; but if I started with a lime compound 

 which originally gave no citron band, I could never by any means, 

 chemical or physical, constrain the lime or the earthy precipitate to 

 yield a citron band. 



The only explanation that I could see for this anomaly was that the 

 elusive citron band was caused by some element precipitated with the 

 calcic oxalate, but present in a .quantity too small to be detected by 

 ordinary chemical means. The calcic oxalate was ignited and 

 dissolved in hydrochloric acid, and fractionally precipitated in three 

 portions with ammonic oxalate, the first and third portions being 

 comparatively small. They were then tested in the radiant matter 

 tube. All three portions showed the citron band, but the portion 

 which came down first gave ?the 'band decidedly the strongest, and 

 the third portion precipitated showed it weakest. 



It having been found that the substance giving the citron band 

 formed a sulphate more soluble in water than calcic sulphate, 4 lbs. 

 weight of commercial plaster of Paris, which showed very 

 faint traces of the citron band, were mixed with water and poured on 



