ANALYSIS. 



as fluxes. The metallic matter, when tlie operation is well 

 coiidufted, is coUefted in a bnttoii at the bottom of the 

 crucible, and its nature and compoiition may be afcertained 

 in the humid way in the ufual maimer by means of the pro- 

 per re-agents, &c. 



In fubmitting an ore to analyfis in the humid way, the 

 general procefs is to digeft it previoufly reduced to powder 

 in different acids. Sulphur, if prefent, is precipitated, or 

 is fomelimcs partially converted into fulphuric acid. If the 

 quantity of fulphur be large, it is beft previoufly feparated 

 as much as pofllble by roafling the ore as above. The 

 refidual matter is then fubmittcd to the aftion of the dif- 

 ferent acids, thefe being often applied fucceffively ; fo that dif- 

 ferent metals, if prefent, are feparated by their proper 

 folvents. The folutions afford by evaporation the metallic 

 falts they contain, or each metal is detefted in the folution 

 by its proper left : it is alfo precipitated by the alkalies and 

 other re-agents, and the precipitate is reduced to the metal- 

 lic ilate, as before, by the aid of fluxes and heat ; or fome- 

 times it may be thrown down at once in the metallic ftate, by 

 another metal having a ft;ronger attraftion for oxygen. 



Thefe are almoll all the general rules that the analyfes of 

 ores will admit of, as the procefles required for different 

 ores differ extremely from one another, and are often very 

 complicated. We refer our readers, therefore, for tha 

 analyfis of particular earthy foffds and ores, to the different 

 ai-ticles in the Cyclopaedia, where they are defcribed. 



Anal^ijis of organ':z.ed Boilies, including vcgcldble and animal 

 "Suhjlances. — The older chemifts attempted the analyfis of 

 organic compounds by diftillation, and thus obtained a 

 variety of refulting fubn.ances equally or perhaps more 

 complicated in their nature than the original fubft;ance to be 

 analyfed. When the theory of chemillry was changed by 

 Lavoifier, that iUuftrious cliemiil began to confider the 

 compofition of organic fubllances in a proper point of view, 

 and he endeavoured to difcover the elements ol thefe bodies, 

 and to determine their proportions. He difcovered the na- 

 ture of their elements, though he was not fo fuccefsful in 

 determining their properties. Lavoifier's principle of ana- 

 lyfis was to oxydize organic bodies till he converted them 

 into binary oxyds, the compofition of which was known, 

 and to perform the experiment in fuch a manner, that the 

 quantity of thefe binai-y compounds with oxygen could be 

 corredlly determined. His mode of operating was to bmn 

 organic fubilances in oxygen gas ; but this method, though 

 jull in principle, did not enable him to determine by the 

 balance with much accuracy, either the quantity of water 

 or of carbonic acid formed by the combuftion ; fo that his 

 refults could be only confidered as approximations. 



Some chemifts, after Lavoifier, endeavoured to determine 

 the exaft quantity of the produfts of dry diftillation, and 

 to calculate from them the compofition of the body. Such 

 was the attempt of Fourcroy and Vanquelin on the compo- 

 fition of urea, and of Dr. Higgins on the acetic acid. 

 But the compofition, and probably alfo the quantity of the 

 produfts of diftillation, being only imperfettly known, it is 

 obvious that fuch experiments, however exaft, can only afford 

 data for calculations hereafter, when the produfts of the diftil- 

 lation come to be better examined and more accurately known. 

 Theodore de Sauflure has analyfed alcohol and ether in La- 

 voifier's manner, and the refults he obtained probably 

 approach nearer the truth than any preceding analyfis of a 

 ternary compound. Thcnard has alfo analyfed different 

 fpecies of ether in the fame manner. 



Th" firft grand ftep, however, towards proportion in 

 the analyfis of organic fubftances, was made by Gay 

 Luffac and Thenard. Thefe celebrated chemifts, in an 



3 



interefting memoir on the fubjeft, after pointing out the 

 difficulties and fources of inaccuracy of the methods then 

 generally employed, gave a defcription of a new method of 

 proceeding, by which they confidered they were able to 

 combine the hydrogen and carbon with the utmoft quantity 

 of oxygen with which they can unite ; and thus, by proper 

 data, to eftimate the proportion of their conftituent parts, and 

 of oxygen exifting in the compound analyfed. The fubftance 

 felefted to furnifti oxygen was the oxvmuriate of potafli, and 

 the matter to be analyfed was mixed with this fait, and defla- 

 grated in an apparatus contrived for the purpofe, confifting of 

 a thick glafs tube, A, ( Plate XXI./^. 3. Chemijlry,) fet ver- 

 tically in a fire, with a lateral tube, B, to condudt the gafes 

 produced to a mercurial apparatus ; and a cock, C, above, 

 the ftopper of which was not perforated, but contained a 

 depreflion, D, into which a portion of the material to be 

 analyfed was introduced ; and by turning the cock down- 

 wards, this portion fell into the tube, and was there defla- 

 grated. E is a veffel containing ice, to keep the upper 

 part of the tube cool. The proportion of the oxymuriate 

 requifite to burn completely the fubftance analyfed was afcer- 

 tained by previous trials in an open crucible ; fo much of 

 the fait being required, that the refidue after deflagration 

 fliould be quite white, or at leaft not carbonaceous ; and iu 

 the aftual experiment a confiderable excefs of the oxymu- 

 riate was employed. The materials were then completely 

 dried, by fubmitting them for a confiderable time to a tem- 

 perature of 21 2°, and afterwards accurately weighed and mixed 

 in a mortar, with a little water, fo as to form an adhefive mafs, 

 which was divided by being thruft into a brafs mould, and 

 the pieces ftiaped by the fingers into little balls, that they 

 might drop clean from the ftopper of the cock down into 

 the deflagrating tube. Thefe balls were dried again at the 

 fame temperature before they were thus burnt. 



The oxymuriate of potafh was itfelf analyfed before it 

 was ufed ; and in order to infure uniformity in its compofi- 

 tion, a confidei-ahle quantity of it was fufed and pulverifed, 

 and kept for ufe. If the fubftance to be analyfed was a 

 vegetable acid, it was combined with lime or barytcs before 

 it was mixed with the fait ; and this calcareous or barytic 

 fait was feparately analyfed, and the carbonic acid remaining 

 united with the earth after deflagration was properly efti- 

 mated. The earthy or other incombuftible matter belong- 

 ing to the fubftance to be examined was alfo feparately 

 eftimated, by calcining this fubftance by itfelf in a platina 

 veffel, and lixiviating the refidue. 



The authors, in their memoir, have given at length all 

 the precautions required in the management of the appara- 

 tus, both in preparing for the deflagration, and in the efti- 

 mation of the gafes obtained ; and after the operation the 

 refults of the analyfis were made out in the following man- 

 ner : " The proportion of combuftible matter in the fub- 

 ftance examined was previoufly found by calcination of 

 another portion of the fame ; the aftual quantity of oxygen 

 employed in the deflagration was known by that of the oxy- 

 muriate ufed ; the carbonic acid was abforbed by potafti, 

 and its carbon eftimated ; the excefs of oxygen was found 

 by fubfequent detonation with hydrogen ; the hydrogen of 

 the fubftance was prefumed to form water with all the 

 oxygen unaccounted for ; and the azote exifted in the refidual 

 azotic gas." 



Soon after the method of Gay Luffac and Thenard was 

 publiflied, Berzelius turned his attention to the fame fub- 

 jcft ; and after beftowing, in his admirable eflay, fomejuil 

 encomiums on the merits of his predeceffors, proceeds to 

 point out fome defefts in the apparatus and methods they 

 employed, and prdpofes new ones of his own. The effen- 



tial 



