THERMOMETER 989 



Mr. Crookes afterwards found the new element in two or three specimens of native 

 Exilphur, and especially in some specimens from the Liparian Islands. Some samples 

 of Spanisli pyrilcs were likewise found to contain traces of the substance. Mr. Crookes 

 called the new element Thallium (from Gr. 6a\\6s, t hallos, ' budding twig'); and 

 described a process by which it may be separated. Thallium is also found in some 

 lithia-micas (lepidolite), and in the Swedish mineral called Crookesite, a selenide of 

 copper and thallium, which contains as much as 19 per cent, of thallium. 



On May 16, 1862, M. Lamy made known the result of his researches and experi- 

 ments on a deposit formed, after the chambers had been fed for a considerable time 

 with sulphurous acid generated by the combustion of Belgian pyrites from the mines 

 of St. Oneux near Spa. M. Frederick Kuhlmann, jun. had extracted several 

 specimens of selenium, one of which he placed at the disposal of M. Lamy. On 

 submitting this specimen to spectrum analysis, M. Lamy observed (early in 1862) 

 the same green line which had been the starting-point of Mr. Crookes' researches. 

 It'thus appears that M. Lamy was led by independent observations of his own to the 

 detection of the green line-producing body previously observed by Mr. Crookes. 

 M. Lamy. however; being fortunate enough to have a very considerable amount of 

 the thalliferous deposit at his disposal, was enabled to pursue his investigation on a 

 proportionately extensive scale. He began a series of experiments -with the view of 

 isolating the element, and soon succeeded in separating very appreciable quantities 

 of the new body, in the form of a metallic ingot. 



For the preparation of the salts of thallium, see Watts's ' Dictionary of Chemistry.' 



THEBAINE. One of the numerous alkaloids obtained from opium. 



THEINE. Syn. Caffeine. C'H 10 N<0 4 (C 8 H 10 KT 4 O 2 ). A feeble base contained in tea, 

 coffee, and, in fact, in most of the plants used in the manner of tea, ; such as Paraguay 

 and Guarana tea. See CAFFEINE and TEA. 



THEWARD'S BLUE, or Cobalt Shie, is prepared by digesting the oxide of 

 cobalt with nitric acid, evaporating the nitrate of cobalt formed, almost to dryness ; 

 diluting it with water, and filtering, to separate some arsenate of iron, which usually 

 precipitates. The clear liquor is to be poured into a solution of phosphate of soda, 

 when an insoluble phosphate of cobalt falls. This being well washed, is to be 

 intimately mixed in its soft state with eight times its weight of well-washed gelatinous 

 alumina, which has been obtained by pouring a solution of alum into -water of am- 

 monia in excess. The uniformly-coloured paste is to be spread upon plates, dried in a 

 stove, then bruised dry in a mortar, enclosed in a crucible, and subjected to a cherry- 

 red heat for half an hour. On taking out the crucible, and letting it cool, the fine 

 blue pigment is to be removed into a bottle, which is to be stoppered till used. 



The arsenate of cobalt may bo substituted, in the above process, for the phosphate, 

 but it must bo mixed with sixteen times its weight of the washed gelatinous alumina. 

 The arsenate is procured by pouring the dilute nitrate of cobalt into a solution of 

 arsenate of potash. If nitrate of cobalt be mixed with alumina, and the mixture be 

 treated as above described, a blue pigment will also be obtained, but paler than the 

 preceding, showing that the colour consists essentially of alumina stained with oxide 

 of cobalt. See COBALT BLUE. 



THEOBRO1VXA CACAO. The Cocoa or Cacao tree : from the seeds of which 

 both chocolate and cocoa are prepared. See COCOA. 



THEOBROMIWE is a chemical principle found in cocoa-beans. It is extracted 

 by boiling with water, filtering, precipitating with acetate of lead, separating the pre- 

 cipitate after washing it, and then decomposing it by sulphuretted hydrogen. 



THEOXiZXTXi. See ABIETKXE. 



THERMO GRAPH Y. A term proposed by the Editor of this Dictionary, in 

 December 1842, to express the 'Art of Copying Engravings, &c. on Metal Plates;' 

 the effect being due in all cases to the influence of heat-radiations. The process is 

 fully described in ' Researches on Light,' by Mr. Eobert Hunt. ' 



THERMOMETER. An instrument used, as its name signifies, as a measure of 

 heat. A description of this valuable instrument belongs to Physics. The principle 

 upon which it is constructed depends upon the expansion of some fluid or solid by 

 heat. We may adopt any body as our heat-measurer, if the rate of expansion is 

 uniform for equal increments of heat, and we determine by previous experiments 

 the rate of expansion to which it is subject, and construct a fixed scale. Usually 

 either mercury or spirits of wine is employed. 



Thermomctrical Table, by Dr. Alfred S. Taylor, F.R.S. The accompanying ther- 

 mometrical table by Dr. A. Taylor has been copied from a thermometer in his pos- 

 session, graduated on the scales of Fahrenheit, Reaumur, and Celsius, or the Centigrade. 

 It has been designed to obviate the necessity for those perplexing calculations, so often 

 rendered necessary by the use of different methods of graduation in England and on 

 the Continent, In most chemical works, we find, besides the rules given for the conver- 



