APPENDIX. 391 



Lead acetate (normal). Saturated solution. 



Litmus solution. Extract the crushed litmus several times with warm 

 distilled water, mix the extracts and filter. Adjust the solution to a neutral 

 tint by means of hydrochloric acid. The sensitiveness of the indicator is 

 much increased by dialysing it against distilled water. A drop or two of 

 chloroform may be added to the solution to prevent the growth of organisms. 



Mercuric chloride. Saturated solution, about 8 per cent. 



Mercuric nitrate. A. To 160 cc. of concentrated nitric acid (sp. gr. 1-42) 

 in a beaker add, in small portions, 220 grams, of red mercuric oxide. Stir well 

 and then add 160 cc. of distilled water. Heat till the oxide has dissolved. 

 Cool and nearly neutralise by adding 75 cc. of N. soda. Make up to i litre 

 and filter. Preserve in a dark-coloured bottle. This solution is used for 

 removing various nitrogenous substances from urine when estimating small 

 quantities of sugar (see p. 345). 



B. To 143 grams, of pure mercury in an evaporating basin add 200 cc. of 

 concentrated nitric acid (sp. gr. 1-42). Heat until thick fumes are evolved 

 and then turn out the gas. When the reaction has ceased light the flame 

 again and evaporate down to about 80 cc. Gradually add about 1500 cc. 

 of water. Cool and make up to 2 litres. 



Mercuric sulphate reagent for tryptophane. See p. 89. 



Millon's reagent. See p. 39. It is usually purchased. 



Nessler's solution. Folin and Denis, Journ Biol. Chem., xxvi., p. 478. 



Phosphotungstic acid. Two per cent, in 5 per cent, sulphuric acid. 



Picric acid, saturated solution, about 1-2 per cent. 



Potassium ferricyanide. Saturated solution, prepared by grinding the 

 solid with cold water in a mortar. 



Potassium jerrocyanide, 5 per cent. 

 Roberts' reagent, see p. 304. 



Sodium hypobromite. Dissolve 100 grams, of caustic soda in 250 cc. of 

 water. Cool. Cautiously add 25 cc. of bromine, cooling thoroughly at 

 intervals. It must be recently prepared. 



Soluble starch. 250 grams, of potato starch is placed in a litre flask. It is 

 treated with a mixture of 375 cc. of water and 125 cc. of pure concentrated 

 hydrochloric acid and the mixture thoroughly shaken until the whole of the 

 starch has been wetted by the acid. It is allowed to digest at room tempera- 

 ture for 8 days, being frequently shaken. The acid is then poured off, the 

 residue repeatedly washed with distilled water and then filtered on a Buchner. 

 To remove the last traces of acid, which inhibit the action of enzymes, it is 

 advisable to suspend the starch in a buffer solution of P H = 7. This can be 

 prepared approximately by treating 50 cc. of 0-2 M. acid potassium phosphate 

 (see p. 24) with 30 cc. of 0-2 N. soda and diluting to 500 cc. After standing 

 for some time with frequent shakings the starch is again washed by decanta- 

 tion with distilled water, filtered on a Buchner and dried in the air. Solutions 

 are prepared in the manner described for starch paste (p. 120). 



Stokes' reagent, see p. 245. 

 Sulphosalicylic acid, see p. 37. 

 Tannic acid, see Almen's reagent. 



Tap grease. Heat together in a crucible on a sand bath i part of soft 

 rubber (free from inorganic filling matter), i part of paraffin wax and 2 to 3 

 parts of vaseline. Stir thoroughly until the rubber has completely dissolved. 



