tion, a brown stain is produced, owing to the reducing action of the uric acid.

138. UREA. CH4N2O (Urine).

1. HNO3, when added to solutions of urea, unites with it, forming the nitrate, which separates out in crystalline plates, which are tolerably soluble in hot water and alcohol, but nearly insoluble in HNO3

2. KHO added to urea decomposes it on heating, and NH3 is evolved.

139. CHOLESTERINE. C26H440 (Biliary Calculi). 1. KHO does not saponify cholesterine, although in many of its properties it resembles oils and fats.

2. Boiling alcohol dissolves cholesterine, and on cooling it crystallizes out in colourless plates.

140. GRAPE SUGAR. CH12O6 (Fruit, Honey, Diabetic Urine, &c.).

1. H2SO forms with grape sugar a definite compound of a yellow colour. No charring occurs as in the case of cane sugar.

2. Solution of grape sugar, when mixed with a few drops of CuSO4 and excess of KHO, produces on boiling a red precipitate (Cu,O), caused by the reducing action of the grape sugar. Solution of cane sugar does not give this reaction until boiled with a single drop of H2SO4, which converts it into grape sugar.

141. Albumin (White of Egg.)

129

1. Boiling water causes albumin to coagulate and it becomes at the same time insoluble, so that if a solution in cold water be heated, coagulation at once takes place.

2. Hg Cl2 coagulates albumin, even when present in exceedingly small quantities. Coagulation also takes place with solutions of other salts, e.g. CuSO4, SnCl2, AgNO3

142. STARCH. CH10O, (Potato, Wheat, &c.). See 43, b.

143. TANNIC ACID. C2H22O17 (Gall-nuts).

1. Solution of gelatin (isinglass) produces a yellowish flocculent precipitate. A piece of animal membrane gives the same precipitate.

2. FeCl produces a dark bluish black precipitate (ink).

144. GALLIC ACID. CHO (Gall-nuts).

1. Solution of gelatin produces no precipitate.

2. FeCl produces in neutral solutions a bluish black precipitate.

145. Detection of CARBON, HYDROGEN, and NITROGEN in ORGANIC BODIES :

(a) CARBON.-Mix the substance intimately with powdered CuO, place in a hard glass tube, fill up with small pieces of CuO, and close the

K

tube with a cork

through which a conducting tube passes into a flask containing clear lime-water. On heating, the carbon is oxidized to CO2, which renders the lime-water turbid. Organic liquids are examined in a similar way : they are placed in a small bulb-tube which is placed inside a hard glass tube and gently heated as soon as the CuO in front is red-hot. In this way the vapour passes over the CuO, and CO, is produced.

(b) HYDROGEN.-Proceed as in a (taking care to use perfectly dry CuO), but connect the conducting tube with a weighed CaCl, tube. Heat the hard glass tube as before, and then weigh the CaCl, tube. Gain in weight indicates that water has been formed by the oxidation of the hydrogen in the substance. When much water is present, it is visible in the bulb of the CaCl2 tube.

(c) NITROGEN.-Mix the substance intimately with powdered soda-lime, and observe if NH, is given off on heating. Ascertain this by the smell and by the action on red litmus paper.

Remove the metals of the Silver, Copper, and Iron Groups by their respective group reagents. Neutralize the solution with (N H4) HO, add Ca Cl, shake well, and allow to stand for at least twenty minutes.

Remaining Acids.

PART V.

REACTIONS OF THE RARE METALS.

147. THE following rare metals are considered here by themselves, and their position in the various groups indicated. For their separation from each other and from the commonly occurring metals, a larger manual must be consulted.

Tungsten, Thallium, Palladium, Rhodium, Osmium, Ruthenium, Gold, Platinum, Iridium, Molybdenum, Selenium,* Tellurium, Uranium, Indium, Beryllium, Zirconium, Cerium, Lanthanum, Didymium, Titanium, Tantallum, Vanadium, Lithium, Cæsium, Rubidium.

* Selenium, although a metallid, is conveniently included here.