HOFAL4NN ON THE CHAXGES OF GUTTA PERCHA. On the CarBonates of Alumina Ferricl Bxide and Chromic Oxide. By James Barratt Esq. (Abstl.mt.)* THEcomposition of the precipitate produced in solutions of sul-phate or chloride of aluminium by alkaline carbonate8 has been varioutdy stated a8 follows :-According to Huspratt (Ohem. Soc. Qu. J. ii 216) it is 3&03 . 2C0 +4HO H. Rose (Pogg. Ann. xci. 462) , A1,03 3H0 -I-HH,.CO,+HO %an lois (Ann. Ch. Phys. {3] xlviii. 502) , 8840,. CO + 8H0 Walfwe (Chem. Gaz. 1858 410) , 3A1 . 2C0 +9HO From experiments made by the author of this paper in Dr. Muspratt's laboratory it appears that the precipitate formed by carbonate of soda in a solution of chloride of aluminium (the mode of preparation adopted by Wallace) after being washed and dried then triturated with water again washed and dried over sulphuric acid consists of hydrate of alumina perfectly free from carbonic acid a result which agrees with the statement of Saussure (Gmelin's Handbook iii.308.) -. Car-bonute of Chmini~ Oxide has been analysed by several chemists. According to Berzelius (Tdt6 iv. 427) it is 4Cr203. C0,+3HO Y3 Meissner (Gilb. Am. lx. 366) lOCr,O . ?'CO,+8HO Langlois (loc. cit.) >) 2Crz03 . CO + 6HO Le fort (Compt. rend. xxvii. 269) 9) CrzOs . COZ+4HO Wltllace (loc. cit.) I * This paper is pnblishcd in fidl in the Chemical Hew 30.10 13. 110. UARRATT ON THE CAiZBONATE OF ALUXINA ETC. 91 Mr. Barratt's experiments confirm the result obtained by Lefort and Wallace.Carbonate of Ferric Oxide.-Soubeiran (Ann. Ch. Phys. [2] xliv. 326) found that the precipitate thrown down by alkaline carbonates from ferrous salts after thorough washing and exposure to the moist air of a cellar for six months no longer contains ferrous oxide but consists of 71.4 p.c. Fe,O, 8.3C0 and 20.0 water (3Fe20,.C02+ 12HO). According to Langlois (loc. cit.) the precipitate formed by alkaline carbonates in ferric salts con- tains when dried at 100" C. 81-47 p.c. Fe203 10.17 NO and 1-36CO, which is given off at 165". L. Gmelin (Randb. v. 222) on the contrary states that this precipitate after thorough washing is quite free from carbonic acid. According to Wallace (loc. cit.) the precipitate thrown down by carbonate of ammonia from ferric chloride contains when dried in the air at 22" to 24"C. 3Fe203.C02+6H0 and gives off 2 eq. water at 100";and the precipitate formed by carbonate of soda in a solution of ferric nitrate is 9Fe,03.C0 +l2HO. Mr. Barratt finds that the precipitate dried in the air at ordi- nary temperatures contains 3Fe,0,.C02 +8H0 half of the water being expelled at 100" C.