Baryta standard

The primary aromatic amines are most readily estimated by means of nitrous acid (see p. 493). Primary or secondary amines, either alone or in presence of tertiary amines, may be estimated by acetylation, since the last do not react. About 1 gm. of the substance or mixture is weighed into a small flask provided with a reflux air condenser, and 5 c.cs. of acetic anhydride added from a pipette having a soda-lime guard tube. In another flask, also provided with a similar condenser, 5 c.cs. acetic anhydride are placed. The two flasks are allowed to stand at room temperature for 30 minutes to 1 hour, after which time 50 c.cs. of water are added to each, and both are placed on the steam bath for an hour in order to convert the remaining acetic anhydride into acetic acid. After cooling, the amount of acetic acid in each flask is titrated with standard sodium hydroxide or standard baryta, using phenolphthalein as indicator. The difference in the two titrations corresponds to the amount of primary or secondary amine present. 

Example.—Mannitol.—The hexa-acetyl derivative (p. 259) is prepared and purified, and a quantity of it—about 0-2 gm.—along with 100 c.cs. of 10% benzene sulphonic acid solution placed in a steam distillation flask. The flask is connected to a condenser on one side and to an apparatus for the generation of pure steam on the other. A suction flask to serve as receiver is attached by a cork to the condenser, and to the side tube of the suction flask a soda-lime tube to prevent the entrance of carbon dioxide is attached. Steam is blown through the flask until (1-5—3 hours) the distillate passing over is neutral. The whole distillate is then titrated with standard baryta, using phenolphthalein as indicator. 

Estimation of Atmospheric Carbon Dioxide.—A convenient method is that of Pettenkofer,4 which consists in introducing a standard solution of barium hydroxide into a large bottle containing several litres of the air to be examined. The bottle is shaken from time to time to keep the sides moistened wit-h the solution, and after 5 or 6 hours the absorption of carbon dioxide may be regarded as complete. The baryta solution is decanted into a small stoppered bottle and allowed to stand until any suspended barium carbonate has settled. A portion of the clear liquid is then removed and titrated with dilute sulphuric acid, using phenol-phthalein as indicator. The diminution in alkalinity due to combination with carbonic acid is thus measured, and from the data obtained the percentage of carbon dioxide m the atmosphere may easily be calculated. 

A colorimetric method has also been devised which is not interfered with by silicic acid. Iron, however, should be removed by means of cupferron. The solution should contain 0-002 to 0-025 milligram of P2Os and 2 c.c. of nitric acid (density 1-12). To this is added 2 c.c. of a quinine solution made by dissolving 1 gram of the sulphate in a slight excess of nitric add and adding enough baryta to precipitate all the sulphate. The colour developed after the addition of the molybdate is compared with that of a standard.3... 

The identification described below depends on chromatographic detection of active phloroglucinol derivatives, especially flavaspidic acid, obtained by concentration using the baryta method. The position of the active substances on the chromatogram is established by cochromatography of a standard solution of resorcinol and phloroglucinol both are commercially available substances which are not present in the drug extract, however. 

Hepburn designed a simple apparatus for the volumetric determination of carbon dioxide, in which the gas, completely evolved from solution under vacuum, is absorbed in baryta water and the residual baryta titrated to phenolphthalein with 0-lN oxalic acid. Standard hydrochloric acid was found to give high results compared with oxalic acid. The time required for absorption was twelve to twenty-four hours. This method has been adopted by the B,P.C. for Effervescent Granules. 

Now prepare 50 or 100 c.c. of a molar solution of the pure acid. If the latter cannot be weighed, e. acetic acid, the strength of the solution must be determined by titration with a standard solution of baryta (p. 162), using phenolphthalein as indicator. Further, two pipettes must be obtained and calibrated, one to deliver, the other to take up, 10 C.C. (p. 35). When not in use, these pipettes should be placed in an upright position, with their ends resting on filter paper. 

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