1815.} in the Physical Sciences. 35 



it, and an acid separates it from the solution in the sLite of an oil. 

 It dissolves in sulphuric and nitric acids. When heated, it does 

 not melt ; but it soon loses its red colour ; it seems to me to be 

 very analogous to linseed oil boiled to dryness. Nothing is known 

 respecting its natural history. It is probably a natural production. 

 It is said to be much employed in Thibet. Whether what is used 

 in the Mediterranean comes from Thibet I do not know. 



2. Cajeput Oil. — This oil has lately acquired considerable cele- 

 brity in some parts of England, as a most ctt'cctual remedy for 

 rheumatism when applied externally to the diseased part by friction. 

 It was first made known in Europe by the Dutch. According to 

 Murray, it was first brought to Holland about the beginning of the 

 eighteenth century. In 1719 it made an article in the Materia 

 Medica in some of the German Pharmacopoeas. It is doubtless an 

 essential oil. Dr. Roxburgh has lately laid a very accurate account, 

 of the tree which yields this oil before the Linnaean Society. He 

 cultivated these trees at Calcutta for about ten years ; so that the 

 doubts still remaining respecting the nature of the plant from which 

 this oil comes may be considered as removed. 



3. Sugar from Starch. — KircIihofF's discovery of the method of 

 converting starch into sugar was no sooner known in Germany than 

 it occasioned a great many publications on the subject, and nume- 

 rous attempts to improve the process, and render this new sugar a 

 substitute for common sugar. These attempts were natural at a 

 time when the mistaken policy of Bonaparte had shut out Europe 

 from all access to foreign countries, and precluded the supply of 

 common sugar, except at an enormous price. I cannot find, how- 

 ever, that any of these attempts were attended with success ; pr 

 that much additional chemical information was even added to 

 Kirchholf's original discovery. This discovery wfis owing to an 

 accident. In consequence of the war between Great Britain and 

 Russia, the Russians found it diflicuU to procure gum. Kirchholf's 

 object was to render starcli a substitute for gum. He thouglit that 

 he would improve it by Ijoiling it in weak sulphuric acid. He 

 gradually lengilicned the Ijoiiing process, in expectation of render- 

 ing the starch more completely gum. The icsult was, that it 

 Hcquired a sweet taste, and tiie properties of sugar. Sclirader lias 

 sliown that by increasing the quantity of sulphuric acid the length 

 of time necessary for boiling may be shortened. 'i1uis five or six 

 parts of suljiluiric acid to 100 parts of starch require only six or 

 eight hours boiling. Nassc found that nitric acid and muriatic acid 

 produce this change on starch as well as sulphuric acid. Starch 

 sugar is not so sweet as common sugar ; but I liave seen it as white, 

 and very like common loaf sugar in appearance. 



4. Su/j (if the Acer Caniprstrc. — In the year 1811 Professor 

 Scherer, of V'ienna, examined the saj) of tiie acer campcstre, or 

 common maple, with a view, I presume, to tlie sugar wl)ieh miglit 

 be extracted fion\ it. 'i'his sap, when in sn)a!l qumitities, wi.s 



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