164 CHAPTER XII. 



reason that lie had omitted from his solutions the essential 

 element, the alumina. He stained, for instance, with pure 

 alcoholic solution of carminic acid, or of carminate of 

 ammonia. Such solutions stain, but stain weakly and 

 diffusely. 



MAYER therefore sought for appropriate means of introduc- 

 ing the necessary alumina into the solutions ; with the results 

 that will be set forth in the next . 



206. Carminic Acid occurs as a purple-brown mass, easily 

 soluble both in water and in alcohol. It ought not to be 

 hygroscopic, nor leave an ash after glowing on a platinum 

 foil. It is (according to NTETZKI, Chemie der organischen 

 Farbstofe, Berlin, 1889, pp. 231 234) a weak (LiBBERMANN 

 says a strong) dibasic acid, which forms soluble salts with 

 the alkaline metals, insoluble violet-coloured ones with the 

 earthy and heavy metals. Very little is known concerning 

 the chemical nature of these salts. 



The alumina salt (carminate of alumina) has the remark- 

 able property of being soluble not only in acids and acid salts, 

 such as alum, but also in alkalies and alkaline salts, such as 

 borax, provided that only water or weak alcohol be employed 

 as the menstruum. It may be obtained by precipitating a 

 solution of carminic acid or of carminate of ammonia by means 

 of acetate of alumina. It is also precipitated from the above- 

 named solutions by chloride of aluminium, but only in part ; 

 whilst if alum be taken no precipitate is produced, the car- 

 minate of alumina remaining in solution, and forming the 

 staining fluid given below under the name of Carmalum. 



When chloride of aluminium is taken, a precipitate is 

 formed, as stated above. But this precipitate will redissolve 

 if more chloride of aluminium be cautiously added. This 

 gives the staining fluid described in 212, which may be 

 convenient in cases in which it is not desirable to work with 

 a fluid containing alum. 



Both of these solutions stain in a violet tone, something 

 like alum-carmine. A redder tone may be obtained by 

 adding calcium chloride to the carmalum solution. But this 

 is not advisable, for calcium chloride added to carmalum 

 precipitates the solution with formation of gypsum. Of 

 course, this does not occur with the aluminium chloride 



