Scientia Sinica

66 SCIENTIA SINICA Vol. V.

(2) Chloropentamminecobaltic chloride, [Co(NH;);Cl] Cl, (purpuro): This is prepared according to the procedure described in Biltz and Biltz’s Laboratory Methods of Inorganic Chemistry™!,

(3) Nitritopentamminecobaltic chloride, [Co(NH;);NO,] Cl, (xantho).

(4) trans-Dinitritotetramminecobaltic chloride, trans-[ Co(NH;),(NO,),] Cl, (croceo). :

(5) cis-Dinitritotetramminecobaltic chloride, cis - [Co(NH;),(NO,),]Cl (ilavo).

The last three salts are prepared according to Jorgenson”. After preparation, these five salts are purified and washed with ether and heated to dryness in an oven at 45-50°.

n-Valeric acid: ‘This is prepared by the following steps: n-butyl alcohol_1y n-butyl chloride 25 n-butyl cyanide | * ysodium n-valerate_* , n-valeric acid.

n-butyl alcohol from Chi Fa Co. of Shanghai is distilled. Step 1 is KBr . method'! and the product, #-butyl bromide is purified once. Steps, 2, 3 and 4 are done according to Adams and Marvel!). The z-valeric acid thus obtained is distilled several times until its density at 25°C is constant. Its physical properties are: b. p., 186.2-186.6°C; D?, 0.93445. Timmermann and Hennaut-Rolland’s values’! are: b. p., 186.35°C; D?’, 0.93465.

_ Standard NaOH solution: A solution of 0.1” (or 0.2”) NaOH is prepared according to standard procedure and stored up in pyrex flask provided with a sodalime tube and an automatic flowing device. It is standardized by benzoic acid or standard HCl solution before use.

Indicators: Phenolphthalein is used as indicator to titrate »-valeric acid in xantho- and flavo-cobaltic chloride solutions. Thymol blue is used as indicator to titrate the acid in the other three salts. Since its colour changes from yellow to blue, it is more suitable for use in red solution as purpuro salt.

Apparatus: Solubility bottle: This is a glass-stoppered bottle of cylindrical shape, made of Chinese Tyrex glass. Its capacity is about 80 cc. After the solution is put in and the bottle glass-stoppered, it is further closed up by a large thin rubber tube and sealed with paraffin.

Thermostat: ‘This is a thermostat of the toluene-mercury regulator type. The rotating axle in the centre of the bath has wing-shaped plates provided with clamps which can hold up the solubility bottle at any angles.

Procedure: 60cc of cobaltammine solution at definite concentration and 4 cc of n-valeric acid are put into the solubility bottle. It is continuously shaken