214 ANNUAL OF SCIENTIFIC DISCOVERY. 



TEST FOR THE SOLUBLE CONSTITUENTS OF GUMS. 



THE so-called gums are complex natural products. In certain kinds 

 two substances have been distinguished the one arabine, soluble in 

 cold water ; the other cerasine, insoluble therein. The former consti- 

 tutes the greater portion of the gum- Arabic and Senegal gum, whilst 

 the latter predominates in cherry-gum and gum-tragacanth. For such 

 gums as consist entirely or partially of arabine, Lassaigne recommends 

 the persulphate of iron and tribasic acetate of lead as tests. The sul- 

 phate of iron precipitates the gum even from solutions of sugar, which 

 has no influence upon the precipitate. This is yellowish, gelatinous 

 and transparent. This result deserves especial attention, as there are 

 other substances soluble in water, which are precipitated by alcohol 

 and basic acetate of lead, but upon which the sulphate of iron has no 

 influence. The precipitate produced by the lead salt and alcohol is 

 liable to be confounded with dextrine, and other gum-like substances, 

 which so frequently occur among vegetable products ; the salt of iron 

 distinguishes arabine from these decidedly. The soluble portion of 

 gum-tragacanth, which is regarded as isomeric with arabine, is precip- 

 itated like arabine, by the sulphate of iron ; but the precipitate by 

 tribasic acetate of lead is white, floculent, opaque and caseous, whilst 

 the gum extracted from tragacanth with cold water furnishes a trans- 

 parent gelatinous precipitate, with basic acetate of lead. In syrup 

 mixed with gum- Arabic the gum can be detected by sulphate of iron in 

 the portion precipitated by alcohol. Dextrine, the gummy constitu- 

 ent which alcohol throws down from commercial starch-syrup, does 

 not furnish with sulphate of iron a precipitate like arabine, so that an 

 admixture of gum is easily detected. Lassaigne, Jour, de Chim. 

 Med. 



ON SOME DISTINGUISHING REACTIONS OF ARSENICAL AND ANTIMONIAL 



SPOTS. 



IF a drop of bromine is placed on a saucer, and a capsule containing 

 arsenical spots inverted over it, the spots take a very bright lemon- 

 yellow tinge in a short time. Antimonial spots, under the same cir- 

 cumstances, are acted upon much more rapidly, (in about five seconds, 

 at a temperature of 52 Fah.,) and assume an orange shade. Both 

 become colorless if exposed to the air, and are again restored if treated 

 with a strong solution of sulphureted hydrogen. The secondary yellow 

 of the arsenical spots, as observed by Lassaigne, disappears on the ad- 

 dition of ammonia, whilst that of antimonial spots remains untouched. 

 A concentrated solution of iodate of potassa turns arsenical spots of a 

 cinnamon-red, and dissolves them almost immediately. On antimo- 

 nial spots it has no visible effect within three or four hours. Solutions 

 of the hypochlorites of soda and lime, and fresh chlorine water, dis- 

 solve arsenical spots instantaneously, leaving those of antimony. A 

 concentrated solution of chlorate of potassa gradually acts upon arseni- 

 cal spots, but not upon those of antimony. The nitro-prusside of 

 potassium, on the other hand, slowly dissolves antimony, producing no 

 perceptible effect on arsenic. /. W. Slater, Chem. Gaz., No. 199. 



