568 CONSIDERATION OF CARBON COMPOUNDS. 



the test in which sulphanilic acid and alpha-naphthylamine are used. In 

 Ehrlich's Diazo Reaction for typhoid fever, it is believed that some unknown 

 phenolic or amino compound in the urine unites with the diazo-sulphanilic 

 acid reagent, and forms an azo-dye. Some of the indicators used in volumetric 

 analysis are azo-dyes, for example, methyl-orange (see page 410). Dimethyl- 

 amino-azobenzol, C 6 H 5 N = N C 6 H 4 .N(CH 3 ) 2 , is used to detect hydrochloric 

 acid in stomach contents. 



Phenyl hydrazine, C 6 H 5 .NH.NH 2 . When diazo-compounds are reduced, 

 they yield derivatives of the mother-substance, H 2 N NH 2 , known as hydra- 

 zine, or diamine. Thus, diazo-benzene yields phenyl hydrazine. It is a 

 strongly basic substance and unites readily with acids to form salts ; it is a 

 colorless crystalline substance, sparingly soluble in water, but soluble in acids. 

 Phenylhydrazine is of interest because it is used in the manufacture of anti- 

 pyrine, and as a valuable reagent for the detection of aldehydes and sugars. 

 It combines with both classes of compounds, forming with aldehydes bodies 

 known as hydrazones, with sugars, osazones. Most of these compounds are solid 

 and crystalline; the crystalline structure often serves for identification. 



Arsenic and phosphorus derivatives. A number of compounds of aro- 

 matic hydrocarbons containing arsenic and phosphorus, and having compo- 

 sitions similar to nitro-, azo-, and amino-compounds, are known. The simi- 

 larities are shown in the following table : 



Arsenobenzene, C 6 H 5 .As : As.C 6 H 5 , is obtained by the reduction of phenyl- 

 arsine oxide, C 6 H 5 .AsO, by phosphorous acid, as yellow needles. By oxidation 

 it is converted into phenylarsonic acid, C 6 H 5 .AsO(OH) 2 . 



Sodium para-aminophenyl arsonate, NH 2 .C 6 H 4 .AsO(OH).ONa.3H 2 O (sodium 

 arsanilate, sodium aniline arsonate, atoxyl), is a white, odorless, crystalline salt, 

 soluble in about 6 parts of water, and having a faint salty taste. The aqueous 

 solution on standing assumes a yellowish tint. It is used in sleeping sickness 

 (trypanosomiasis), syphilis, malaria, etc. It should be given hypodermically, 

 and not by the mouth. Atoxyl is made by heating aniline arsenate to about 

 200 C. for several hours, when a reaction takes place analogous to that by 

 which para-amino-benzene sulphonic acid (sulphanilic acid) is formed by heat- 

 ing aniline sulphate : 



C 6 H 5 NH 2 .(HO) 3 AsO = NH 2 .C 6 H 4 .AsO(OH) 2 + H 2 O 

 Aniline arsenate. Para-aminophenyl arsonic acid. 



The sodium salt of this acid is atoxyl. 



IKoxydiaminoarsenobenzene, ^ ) ^C 6 H 8 .Afl : As.C 6 H 3 <^^^ ffi. The 



dihydrochloride ("bichloride," as it is called in the market) of this diamine 

 compound was prepared by Ehrlich and Bertheim, and was the 606th com- 

 pound made in a search for a specific remedy for germ diseases. It is known 

 as " 606," or salvarsan. The arsenic occupies the para position in the benzene 



