MICROCHEMIS TRY. 131 



This reaction was used on Spirogyra by Loew and Bokorny 

 (I, 194) by first placing the plant in a .2% caustic potash 

 solution for half an hour to an hour, then, after washing, in 

 a 10% solution of copper sulphate for an hour, and finally, 

 after repeated washing on the slide, moistening with a 2 % 

 caustic potash solution. 



C. Alloxan, Mesoxalylurea, C 4 H 2 N 2 O 4 . 



229. Alloxan has lately been proposed by Krasser (I, 18) 

 as a reagent for proteids. It is added, preferably to pre- 

 viously dried sections, in concentrated aqueous or alcoholic 

 solution. It then colors most proteids purple-red, and, ac- 

 cording to Krasser, this color is not changed by concentrated 

 caustic soda. But the reaction is hindered by free acids. 

 Of the other organic substances which Krasser has treated 

 in the same way, unfortunately without enumerating them 

 in his publication, only tyrosin, asparagin, and aspartic 

 acid gave the same reaction ; and it therefore seems to be 

 caused by the molecular group common to these substances, 

 H 2 .CHNH 2 .COOH. 



But, as Klebs has shown (IV, 699), the value of this reac- 

 tion is very slight ; for various inorganic compounds like 

 phosphates and bicarbonates of the alkalies give a very deep 

 red color with alloxan, and alioxan itself turns red on evap- 

 oration in the air ; and this color, as well as that produced 

 with proteids, is changed to violet by caustic soda, according 

 to Klebs. 



77. Aldehydes. 



22pa. Various aldehydes, especially salicylic aldthydc, 

 C,H 4 OH.CHO, anisic aldehyde, C 6 H 4 .OCH 3 .CHO, vanillin, 

 C 6 H 3 .OH.OCH 3 .CHO, and cinnamic aldehyde, C 6 H 5 .CH : 

 CH.CHO, have lately been recommended for the micro- 

 chemical recognition of albuminoids by Reichl and Mikosch 

 (I, 34). The objects to be tested are first left for 24 hours 

 in a J \<f> alcoholic solution of the aldehyde used, and then 

 placed on the slide in a mixture of equal volumes of water 

 and sulphuric acid, to which a few drops of ferric sulphate 



