L'examen des alcools amyliques pour gerber

Abstract - After making a review of the purity requirements applied in Belgium and other countries, the author comments the results of many controls of amyl alcohols for the Gerber fat determination.
The specific gravity's determination detects only the water and the inferior alcohols contents.
The distillation's curve is also chiefly influenced by those alcohols.
Distillation is very difficult to be realized correctly.
Preferably it can be replaced by gas-chromatographic estimation which gives more easily better indications.
None of theses methods above mentioned detects the oily substances, furfural and other organic impurities.
Specific tests for these substances are often very difficult to be interpreted.
The blank test is no more satisfactory.
According to the author, only the comparative Gerber tests on milk are to be retained practically.
He proposes to specify as next the physico-chemical characteristics of the amyl alcohols for Gerber:
Amyl alcohol: specific gravity at 20° C: 0,81 - 0,82 g. / mL.
The amyl alcohol is to be composed from a chemically pure mixture of the two primary alcohols 3-methyl butanol-1 and 2-methyl butanol-1 (min. 95 per cent).
Other inferior alcohols as butanol-1 of 2-methyl propanol-1 may be present. (max. 2,5 per cent iso-butanol).
The quantity of impurities cannot be such as the amyl alcohol cannot fulfil the following suitability test:
Suitability test:
The fat contents of 3 milk samples with different contents (3 ± 0,5 per cent) are determined, according to Gerber, using on one side the amyl alcohol to be examined and on the other side a pure amyl alcohol, composed only from the two above mentioned primary alcohols. (eventually prepared by distillation).
The fat determinations are made in triplicate in selectioned butyrometers. (scale error < 0,03 per cent).
The difference between the mean values of the nine in each of the series obtained results may not reach 0,03 per cent

Résumé - Après avoir rappelé les exigences de pureté requises en Belgique et à l'étranger, l'auteur commente les résultats de nombreux contrôles d'alcools amyliques pour Gerber.
Les épreuves de distillation et autres tests couramment proposés ne donnent des indications valables qu'à condition de réaliser une longue suite d'essais divers.
L'analyse chromatographique en phase gazeuse fournit des renseignements très utiles mais incomplets.
En conclusion, l'auteur retient, comme test pratique, les essais comparatifs sur laits. A condition de disposer d'un alcool amylique valable, pris comme réactif de référence, l'épreuve de conformité peut se ramener à de simples déterminations acido-butyrométriques parallèles