2 TECHNICAL BULLETIN 2 3 8, U. S. DEPT. OF AGRICULTURE 
were made with two American companies to supply the poison in 
commercial quantities. A number of reports by field agents of the 
Bureau of Biological Survey have already indicated the value and 
use of thallium products in field practice. The difficulties encoun- 
tered by E. E. Horn, district investigator in the control-methods 
research project of the bureau, in obtaining acceptance by rodents of 
certain thallium baits led to the study of six commercial thallium 
products. 
The methods employed in the feeding tests are essentially the same 
as those used in the previous pharmacological and toxicological 
studies of other rat poisons (arsenic, strychnine, barium carbonate, 
and squill) undertaken cooperatively by the Bureau of Biological 
Survey and the pharmacolog}^ laboratory of the Bureau of Chem- 
istry (now the pharmacology unit of the Food and Drug Admin- 
istration). The literature on thallium through 1896 was listed by 
Doan {63).^ In the present bulletin, all available information in 
the literature has been consolidated, as well as the results of the 
feeding experiments with thallium compounds conducted by authors. 
So far as possible the original articles have been consulted. 
REVIEW OF THE LITERATURE ON THALLIUM 
OCCURRENCE AND PROPERTIES 
Crookes (53) extracted thallium with selenium from the deposit of 
a sulphuric-acid factory at Tilkerode, in the Harz Mountains, Ger- 
many. When examined spectroscopically, a new spectrum was ob- 
tained in which a green line at 1442.6 on the Kirchhoff scale, cor- 
responding to A= 5,350.7 A, was the outstanding characteristic. 
Since the green line recalled the fresh color of vegetation in spring, 
Crookes named the new element " thallium " from the Greek daWos 
(a young shoot). This discovery was announced in 1861. Lamy, 
two years later (94-), observed the green spectral line from the sul- 
phuric-acid deposit at Loos, France, where Belgian pyrites were 
roasted. He claimed that 0.000,002 milligram of thallium could be 
detected by its flame spectrum (107) . 
Uncombined thallium has not been found. It has been estimated 
that the hydrosphere and lithosphere of the earth contain less than 
one part of thallium per billion, and it is not shown in the solar 
spectrum {107). Lorandite (TlAsSs), from Macedonia, contains 
59.5 per cent of thallium associated with realgar. . Urbanite, from 
Macedonia, contains 30 per cent of thallium. Hutchinsonite, a 
sulpharsonide of thallium, lead, silver, and copper, contains an 
appreciable quantity of thallium. The Swedish mineral crookesite, 
with a composition agreeing with (Cu, Tl, Ag)2Se, contains 16 
to 18.5 per cent of thallium. Fractions of 1 per cent have been re- 
ported in cupriferous pyrites from various sections of the world; 
and also in lepidolite, zinc blende, pitchblende, pyrolusite, manga- 
nite, carnallite, certain mineral waters, natural sulphur, and many 
minerals. It has been obtained from lead-chamber deposits in the 
manufacture of sulphuric acid by the roasting of pyrites or raw 
sulphur {88, 108). 
' Italic numbers in parentheses refer to Bibliography, p. 21. 
