124. Mr. J. Dalton on the Nature and Properties of Indigo. 

 diTo in this state for oxygen, that it resumes it from atmo- 

 spheric air the moment they are brought mto contact 

 ^ Pure indiao thus obtained is called precipitated m^xgo . the 

 solu on n^ay also be had from a blue-dyer's vat by plungmg 

 an empty phial into the liquid a few inches be bw the surface. 



The^ other way of obtaining pure indigo is by subhmat>on. 

 Take 20 or 30 grains of pulverized common md, go and place 

 it in an iron spoon, which must be gradually heated to 500 or 

 6oS° "ahrenlfeit. A purple smoke will then -hab -pously 

 and at the same time a fine tissue of small, shining, si ky 

 needles will start up on the surface of the indigo. These may 

 Te wiAdrawn by the point of a knife ; they are crystals of sub- 



^""p^-'^Zed and Mned indigo appear by ^be ^hem^^^^^^ 

 tests to be constituted of the same elements; and no doubt ,s 

 Entertained that they present the pure colouring mattei of 

 indi"-o in its most concentrated form. - r -. „,;il, 



Tliree chemists have published analyses of pure '"'^ SO w.Ui- 

 in the last three years; namely, Drs. Thomson and Uie, and 

 Mr W C mu' all of Glasgow. The same plan was adopted 

 bvkll three ; namely, burnhig a small given portion of indigo 

 x^ncm tact w th the black oxicfe of copper in green glass Uibes. 

 Tirndgo being finely divided and intimately diffused 

 thougha^omparatively large portion of the ox.de heat s 

 applie"d sufficient to burn the carbon and hydrogai of le.n- 

 diio and to liberate the azote: hence from the quantities ol 

 c^bonlc acid and azote produced, and the loss o we^ which 

 the oxide sustains, the constituents of ind.go ai e infei i ed. 1 He 

 results are below : Dr. Thomson. Dr. Ure. ^r. Crum. 



Carbon 40-39 — 71-37 — /S22 

 Azote 13-46 - 10 - 1-26 



Oxygen 46-15 - 14-25 - 1260 

 Hydroge n — _!!?. — _f-±l 



100 100 100 



It is observable that the results of Dr. Ure and Mn Cn.m 

 present no remarkable differences, except m regard to hytl o- 

 Sen wl "ist Dr. Thomson finds no hydrogen : and remarkable 

 iiffe'rences between his results and those of the other two are 

 found in the articles carbon and oxygen. ., • „c 



The atomic constitution of indigo by the above authors .s as 

 follows: Dr. Thomson. Dr. Ure. ^^'•- C-- 



Carbon 7 atoms - 16 atoms — 16 atoms 



»^aruou ( cii-w.w.. 



Oxygen 6 do. _ 2 do. - 2 b. 

 A'it^e 1 do. - 1 do. - do. 



6 do. — ^ 

 "25" 23 



Azote >■ ""■ ' , A An. 



Hydrogen_0_ do. — _6_ do. — 4 do. 



14 



I nni 



