446 SCIENCE PROGRESS 



the presence of halides, is of importance. The test depends 

 on the production of a yellow or orange colour on rendering 

 alkaline the nitro-salicylic acids formed by a nitrate and 

 salicylic acid in presence of concentrated sulphuric acid. The 

 reagent consists of a 7 per cent, sulphuric acid solution of 

 salicylic acid, and a few drops of this are warmed with a small 

 amount of the solution to be tested. On cooling and making 

 alkaline, the colour will be produced. Another colorimetric 

 test which may prove very useful in analysis has been dis- 

 covered by Sacher (Chem. Ztg. 191 5, 39, 319). One part of 

 manganese in 200,000 parts of solution may readily be detected, 

 if the Mn(OH) 2 precipitated by alkali is allowed to oxidise 

 partially in the air and then treated with drops of a N/2 oxalic 

 acid solution. A sharp red colour results, which is stated as 

 being due to the formation of a double salt. Presence of 

 reducing agents, tannic acid, excess of oxalic acid, and high 

 temperatures must be avoided, but as such conditions are 

 required in the separation of manganese by the ordinary 

 table, the test is valid to detect traces of the metal. 



A further improvement in the method of analysis in Group 

 III B has been effected by Atack's test for cobalt with the 

 sodium salt of a-nitroso-/3-naphthol (J. Soc. Chem. Indust. 

 191 5, 34, 641). In the presence of dilute sulphuric acid this 

 reagent is capable of detecting cooi mg. Co per c.c. by the 

 production of an orange-red coloration. The test can be 

 applied in the presence of nickel, ferric, manganese, and zinc 

 salts, and tartaric and citric acids, although it is first neces- 

 sary to remove any large amounts of nickel which may be 

 present. 



A modified method of testing for strontium and calcium in 

 Group IV has been suggested by Gilmour {Chem. News, 191 5, 

 111, 217), which surmounts the difficulty of having to separate 

 strontium before the oxalate test for calcium can be applied. 

 Barium is separated in the usual way by potassium chromate 

 precipitation. Strontium and calcium are then reprecipitated 

 as carbonates, dissolved in acetic acid and neutralised with 

 ammonia. One portion of this solution is tested for strontium 

 by means of calcium sulphate solution, the other for calcium 

 by adding a saturated solution of potassium ferrocyanide, 

 which gives a precipitate of calcium potassium ferrocyanide, 

 whilst strontium gives no such precipitate. 



