86 



PRACTICAL PHYSIOLOGY. 



[X 



Preparation of Leucin and Tyrosin. — Place 2 parts of horn shavings 

 {h-i kilo.) in a mixture of 5 parts of concentrated sulphuric acid and 13 parts 

 of water. Boil for twenty-four hours in a vessel placed in connection with a 

 condenser. Add thin milk of lime until a feebly alkaline reaction is obtained, 

 filter through flannel, re-extract the residue with water, mix the filtrate and 

 washings and slightly acidulate them with oxalic acid. Filter to remove the 

 oxalate of lime, and evaporate the filtrate until a scum forms on the surface. 

 Cool and repeat the evaporation process until crystallisation ceases to take 



place in the mother-fluid. Collect the 

 mass of crystals, dissolve them in boiling 

 water with the addition of ammonia, and 

 add lead acetate until the resulting pre- 

 cipitate is no longer brown, but becomes 

 white. Filter, acidulate the acid filtrate 

 feebly with dilute sulphuric acid, filter oft 

 the lead sulphate and allow the fluid to 

 cool, when tyrosin in an almost pure form 

 crystallises out. 



The mother-liquor, freed from tyrosin, is 

 treated with sulphuretted hydrogen to get 

 rid of the lead, filtered, evaporated, and 

 boiled for a few minutes with freshly 

 precipitated hydrated copper oxide, which 

 Fig. 44.— Crystals and Sheaves of Tyrosin. forms a dark blue solution. The latter, 



when filtered and evaporated, yields blue 

 crystals and an insoluble compound of leucin-copper oxide. This deposit and 

 the crystals are decomposed in water by H.^S- solution, the filtrate when 

 necessary decolorised by boiling with animal charcoal, again filtered and 

 evaporated to crystallisation, when leucin crystallises out. It is obtained 

 pure by recrystallisation from boiling alcohol {Drecltsel). 



14. Tyrosin is insoluble in alcohol and in 1000 parts of cold water. 



(a.) Observe microscopically its crystalline form, as fine long silky needles 

 arranged in sheat-like bundles (fig. 44). 



{b.) Boil a hot watery solution with Millon's reagent (avoid excess) = a red 

 colour {Hoffman's test). 



15. Leucin. — (o.) Under the microscope observe it in the form of brown 

 balls, with radiating and concentric lines it it is impure ; and, when it is 

 pure, as white shining lamellne, with a fatty glance. It is soluble in 27 parts 

 of cold water, and much less soluble in alcohol, 



(6.) Heated in a tube it sublimes unchanged in very fine clouds with tha 

 odour of amylamine. A part is decomposed into COg and CjHjaN (amylamine). 



