292 Croconatc of Copper. — Fatti/ Acids. 



with Fourcroy's experiments, according to which, caoutchouc 

 is precipitated from the milk-saps by the oxidizing action of 

 the atmosphere. {Journal fiir Praldische Chemie, xxi. p. 

 43-54-.) 



Croconate of Copper. 

 According to L. Gmelin, when warm aqueous solutions of 

 the croconate of potash and hydrochlorate or sulphate of 

 copper are mixed, and the liquid let to cool, small rhombic 

 prismatic crystals of the croconate of copper are deposited. 

 They have a lively semi-metallic lustre, reflect light dark blue, 

 transmit it of a brownish yellow. The powder is of an in- 

 tense lemon-yellow colour. On being heated in a tube they give 

 off water, then decompose violently under evolution of gas; 

 the parts driven out of the tube burn vi^ith showers of sparks. 

 The products of this decomposition are, first, a mixture of 

 carbonic oxide and carbonic acid in variable proportions; 

 second, an empyreumatic faint yellow acid fluid which smells 

 of pyroligneous acid, colours the salts of iron brown, those of 

 silver red (aldehydic acid?); third, a dull brownish-black 

 coallv residue, which on being heated, exposed to the atmo- 

 sphere, burns lively to metallic copper and then to oxide. 

 When the croconate of copper is heated in the atmosphere it 

 gradually decomposes with slight explosions and showers of 

 sparks. The analysis of the crystals, washed with cold water 

 and dried in bibulous paper, gave C 23-36, H 2-23, 43-4.], 

 Cu O 31 '00. The formula for the crystallized salt is, there- 

 fore, C' 0+ Cu O, + 3 H'^ O. Of the three atoms of water two 

 are expelled at 162°, the last does not go off without decom- 

 position. [Annalen der Pharmacie^ xxxvii. p. 58-65.) 



The. Fatty Acids. 

 An examination into the action and constitution of a series 

 of fat bodies has been made under the guidance of Professor 

 Liebig, the results of which have appeared in various num- 

 bers of the Annalen der Pharmacie for IS-iO. The questions 

 to be solved were, do the solid fats, which contain not a trace 

 of margaric acid, give margaric acid on dry distillation ? How, 

 and in what manner, can margaric acid originate from stearic 

 or oleic acid ? This question presupposed the most accurate 

 knowledge of the composition of stearic, margaric and oleic 

 acids. Professor Redtenbacher undertook the examination 

 of stearic acid, and of the acid in the drying oils ; Dr. Var- 

 rentrapp that of margaric acid, the oleic acid in the greasy 

 oils, human fat, olive oil, and in almond oil. Connected with 

 this question was the examination into the origin of sebacic 

 acid, and of the substance characterized by its penetrating 

 smell, to which Berzelius has assigned the name of Akrolein, 



