Hydrochloric acid, determination phosgene

It is, of course, obvious that this method cannot be employed for the determination of small amounts of hydrochloric acid in phosgene. 

Hydrochloric acid and chlorine do not interfere with the determination of phosgene by this method. 

In order to determine phosgene in a gas mixture containing chlorine and hydrochloric acid by this method it is necessary to pass the gas mixture first through three U tubes. The first of these (that is, the one which the gas mixture first enters) contains calcium chloride, the second metallic antimony, and the third zinc dust. ... 

If Kdlliker s apparatus is used to determine phosgene in presence of hydrochloric acid, zinc dust cannot be used as it has too great a resistance. In this case the gas mixture to be tested is first passed through a wash bottle containing a sulphuric acid solution of silver sulphate (3 gm. in 100 ml. sulphuric acid of S.G. 1 84) and then through the acetone solution of sodium iodide. 

If this acid is present in considerable quantity, it may be determined quantitatively by the gas-volumetric method of Berthelot, which consists in absorbing the hydrochloric acid in a small quantity of water. Measurement of the volume of the phosgene before and after the treatment with water gives the quantity of hydrochloric acid present in the sample. In this determination the hydrolysing action of the water on the phosgene may be neglected, for the small quantity of phosgene hydrolysed produces an equal volume of carbon dioxide. 

This reaction forms the basis of a method for the quantitative determination of methyl chloroformate which consists essentially in treating the substance to be tested with aniline solution and titrating the hydrochloric acid formed. In this case it is not possible to determine the carbamic ester formed gravimetrically (as in the phosgene estimation), for it is very soluble in water. ... 

Iron impurities (arising from equipment corrosion) in the residues obtained from the evaporation of a known quantity of phosgene are dissolved in hydrochloric acid, and the iron determined colorimetrically with thioglycollic acid, according to standard procedures. 

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