ANALYSIS OF TISSUES 595 



The acetone distils from the first flask, is freed from phenol and volatile 

 organic acids by passing through the caustic alkali and is precipitated in the 

 receiver as keto-mercury compound. The distillation is continued for 5 

 minutes after the first appearance of a turbidity in the receiver. When the 

 heating is discontinued the glass rod is removed from the rubber piece of 

 tubing so as to prevent back suction of the liquids. The adapter is discon- 

 nected, rinsed out and the precipitation is allowed to complete itself by 

 standing for 10 minutes. 



The precipitate is filtered off through* a thick filter paper or asbestos mat 

 in a Gooch crucible, the pores of which have been closed by first filtering an 

 aqueous suspension of talcum. The first runnings, if turbid, must be passed 

 through the filter again until a clear filtrate is obtained. The flask and pre- 

 cipitate are washed with distilled water until the washings are free from silver. 

 The precipitate together with the filter paper or asbestos mat are transferred 

 from the crucible by means of a pointed glass hook to a clean flask or beaker 

 and any particles adhering to the crucible or hook are washed in with a jet of 

 acid mixture. 1 More acid mixture is added so that the volume used altogether 

 is about 10 c.c. i c.c. of *2N potassium permanganate solution is added and 

 the contents of the flask boiled for 1-2 minutes till they are colourless. It 

 is better to add a few drops of permanganate during the boiling so that a 

 persistent brown colour is present and to decolorise by adding a few drops of 

 strong yellow nitric acid. The contents of the flask are cooled and titrated 

 with *iN thiocyanate solution 2 (about T per cent. KSCN ; i c.c. = i mg. Hg), 

 using 2 c.c. of saturated ferric alum solution as indicator until a brownish tinge 

 ^appears. A control beaker containing i drop excess of thiocyanate should be 

 at hand for comparison. 



A 



i c.c. *iN KSCN = 'ooi gm. Hg = '0058 gm. acetone (Scott- Wilson). 

 ,, = "00644 (Marriott). 



Micro Analysis. 



The above methods are not suitable for the estimation of the acetone 

 and aceto-acetic acid in small amounts of blood, but the Scott-Wilson 

 method can be adapted to the estimation of 0*2 -'05 mgm. acetone as shown 

 by Marriott. 3 With such small quantities of acetone the reagent gives a 

 turbidity which can be compared in a nephelometer with the turbidity given 

 by a standard acetone solution containing '5 mgm. Folin and Denis 4 

 find that the turbidity comparisons can be made with a Duboscq colori- 

 meter thus avoiding the use of the nephelometer. The colorimeter must 

 be carefully adjusted to the light so that the two fields are perfectly alike 

 when a standard suspension is read against itself. It is preferable to have 

 the light coming through a hole in a dark (gfeen) window shade so as to ex- 

 clude the interference of more or less bright objects. 



In mixing the solutions in which the suspensions are formed they must 

 not be shaken, but only gently rotated or inverted. 



The procedure of Folin and Denis with small quantities of urine can be 

 adapted to the estimation in blood, following Marriott's preliminary treat- 

 ment to remove the proteins : 



The air current method using test tubes (p. 556) is used. The pre-formed 

 acetone is obtained by aeration of the cold solution ; if the solution be warmed 

 both the pre-formed acetone and that from aceto-acetic acid is obtained ; 

 finally acetone is obtained from hydroxybutyric acid by oxidation with bi- 

 chromate (p. 598). The comparison is made with the precipitate formed 

 by a standard acetone solution containing '5 mgm. 



1 40 parts HNO 3 , 5 parts H 2 SO 4 , 55 parts H 2 O. 



2 This may be standardised against mercuric nitrate. 



3 J, Biol. Chem., 1913, i$, 289, 293 ; 1914, 18, 507. * Ibid., 1914, 18, 263. 



