Chemistry : general, medical, and pharmaceutical including the chemistry of the British Pharmacopœia a manual on the general principles of the science, and their applications in medicine and pharmacy / by John Attfield.

  • Attfield, John, 1835-1911.
Date:
1881
Catalogue details

Licence: Public Domain Mark

Credit: Chemistry : general, medical, and pharmaceutical including the chemistry of the British Pharmacopœia a manual on the general principles of the science, and their applications in medicine and pharmacy / by John Attfield. Source: Wellcome Collection.

    694/850 (page 660)
    is first converted into KON or NaON, with potash or soda. The following equations, etc., explain the reactions :— 2HCN + 2NaH0 = 2N&m + 2H3O 10)^ 10)987 5-4 9-8 2NaCN + AgNOg = AgCN,NaCN + NaNOg lOygs 10)170^ 9'8 17' — grammes in 1000 c. c. of standard solution. It is seen that 54 grammes of real hydrocyanic acid (HCy) are equivalent to 9'8 grammes of cyanide of sodium, and repre- sent 17 grammes of nitrate of silver, or 1000 c. c. of standard solution of nitrate of silver. The cyanide of sodium having been obtained, the titration is caiTied on until it is converted into the soluble double salt (NaCy, AgCy), immediately after which a permanent tur- bidity occurs, due to precipitation of cyanide of silver, thus :— AgCy,NaCy + AgNOg = 2AgOy + NaNOg. This turbidity affords a delicate and satisfactory proof of the completion of the above reaction. There is, however, a difiiculty in the conversion of the acid into the cyanide (Siebold), to which it is necessary to pay particular attention. Tincture of litmus is added to the acid diluted largely with water, and the soda poured in. Owing to the strong alkaline reaction of the cyanide of sodium formed, the mixture becomes blue when only a small pro- portion of the acid has been converted. If then the titration be conducted until the turbidity appears, only the cyanide of sodium will be estimated, leaving free hydrocyanic acid still unacted upon. Indeed, cyanide of sodium may be estimated in presence of hydrocyanic acid in this way. Thus the following reaction (expressed approximately) might occur:— NaCy + 4HCy + AgNOg = AgCy + NaNOg + 4HCy V ' ^ , ' Alkaline. Turbid and acid. In this case only one-fifth of the acid originally present would be estimated. The mixture would, however, become acid. If this acidity be prevented all difficulty is overcome. The following details (Senier) will be found to answer well. To the diluted hydrocyanic acid add soda solution to a strong