Turbidity temperature of oils and fats with glacial acetic acid

E. W. T. Jones
1894 The Analyst  
THIS test, due to Valenta, is described by him in J. C. S., dvi" p. 1078, where he also gives results on certain oils. I have been investigating this test, and although the hopes I had entertained of its usefulness, as an independent and totally distinct test for differentiating between those butters which, although genuine, are low in the usual butter characteristics according to chemical testing, and actual mixtures approximating such butters, have not been realized, I have ascertained a few
more » ... ascertained a few facts concerning the test which I think are worth recording. Valenta indicates the requisite strength of the acid by specific gravity, which he gives as 1056.2. This, according to the most reliable table I can find (Oudeman's), may mean 44 per cent. HA, or 99.7 per cent. HA. Of course the former strength is not " glacial," but I shall show that specific gravity is altogether inadequate to determine the fitness of the acid for oil-testing; indeed, it will need no further demonstration when I mention that 4 C.C. of water, added to 2,300 C.C. (a Winchester quart) of acid, lowered the turbidity temperslture 5" C. This nieans that a difference of less than 0.2 per cent. in the HA effects this divergence, and it follows that a very small dilution of the strongest acid may make it absolutely useless for the test at all. The turbidity temperature, say, with a known sample of butter-fat, is the most delicate test I know of for adjusting the requisite strength of this strong acetic acid for the purpose in view. An acid which by titration contained 98 per cent. (97.99) of HA gave with a butter-fat a temp. of 48" 6 . ; the addition of 2 per cent. of water made it over 100" C.-quite unfit for use ; 1 per cent. made it 79" C., whilst 0.2 per cect. made it 55" C. This shows the importance, if this test is to be used to give at all cornparable results, of adopting a scheme to secure exactly the right strength of acid, and the following is the course I have followed. I have carefully filtered off some fat from a normal butter into a bottle, and this I employ to set every fresh batch of acid I use. I procure the best and strongest glacial Ecetic acid, and suppose I find it gives a temp. of 50" C. with my standard butter-fat, I carefully add water until the temp, with it is 60" C. ; thus I know that whatever tests I inake with this acid are strictly comparable with any previous tests I have made. I t is most important, too, that the relative proportions of the acid and fat or oil are pretty strictly adhered to, and absolutely necessary that the set proportion of the fat or oil to the acid is not exceeded ; any error in measurement should lean to the full measurement of the acid, which does not make the difhrence that the converse proportion does. I make special pipettes, a narrow one delivering 3 gramines of water at 155°C. for the acid, and wider ones, with wider orifices, delivering
doi:10.1039/an8941900151 fatcat:dftyg5bsnvab7mdfo3g3ullumu