Bauhaus-Universität Weimar

Handbook for the Physiological Laboratory. Text
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
tion, then disconnect the glass tubing, and after attaching a clean 
piece, pass them into Nessler’s reagent and then into water. 
The baryta will be precipitated as white carbonate, the 
Nessler’s reagent will become brown, showing the presence of 
ammonia, and the water in the third test-tube will acquire the 
peculiar smell of amylamine and an alkaline reaction. Add to the 
barium solution a little nitric acid. It will become clear and 
evolve gas, showing that the precipitate was barium carbonate. 
A minute quantity only of NH3 is disengaged when leucine is 
heated alone, and the coloration of Nessler’s reagent is there¬ 
fore very slight. If a little lime and caustic soda or potash are 
heated with the leucine much more NH3 is given off. 
36. Preparation of Nessler’s Reagent.—Dissolve 4 grammes 
of potassium iodide in 250 cub. cent, of distilled water. Set aside 
a few cub. cent., and add a cold saturated solution of mercuric 
chloride to the remainder, till the precipitate of mercuric iodide 
is no longer dissolved on stirring. Add that part of the potas¬ 
sium iodide solution which was set aside, to the rest, so as 
to dissolve the remaining precipitate, and then add mercuric 
chloride again very gradually, till a slight permanent precipitate 
is produced. If a few cub. cent, of the potassium iodide solution 
were not set aside, great caution would be required in adding the 
mercuric chloride so as to avoid excess. Dissolve 150 grammes 
of potassium hydrate in 150 cub. cent, of distilled water, allow 
the solution to cool, and add it gradually to the potassium iodide 
solution. Pour the mixture into a measuring-glass or flask, 
and add distilled water to make up a litre. Pour it into a large 
well-stoppered bottle, taking care that there is no ammonia near 
it at the time. It will deposit a brown precipitate, and become 
quite clear and of a pale greenish-yellow colour. It is then 
ready for use ; a little of it should be poured into a smaller bottle 
when wanted. 
37. Detection of Leucine in Tissues.—In order to detect the 
presence of leucine, cut up the organ (the pancreas of a sheep or 
ox, for example) into small pieces with a large knife or sausage- 
making machine. Mix it with water and let it stand for a little 
while, stirring it frequently ; filter it through a piece of cloth, and 
press out the water first with the hand, and then with a screw- 
press. Extract it with water a second time in the same way. 
Mix the watery extracts together, acidify slightly with acetic 
acid, and boil, to coagulate the albumin. Filter : add a solu¬ 
tion of lead acetate to the filtrate. Filter: pass sulphuretted 
hydrogen through the filtrate to remove the excess of lead. 
Filter : evaporate the filtrate to dryness. Extract the residue 
with boiling alcohol. Filter : evaporate the filtrate to a syrup,


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