APPENDIX. 389 



4. Titration. Determine the amount of acidity in the distillate by titration 

 with a standard solution of caustic soda or potash, methyl orange being used 

 as an indicator of the end of the reaction. Methyl orange gives a pink with an 

 acid, and yellow with an alkali. 



The apparatus used in the Physiological Laboratory of Owens College is 

 that made by Messrs Baird and Tatlock (see their catalogue), and is so 

 arranged that several estimations can be made simultaneously.. Other modi- 

 fications are in use. 



Example. Suppose o. 15 gramme of the N-substance has been treated with 

 acid, neutralised, and the ammonia distilled over and received by 100 cc. of a 

 decinormal solution of HC1 ( 10 cc. normal acid). The distillate is then treated 

 with decinormal caustic soda, and suppose it is found that the neutral point 

 is reached when 60 cc. of the decinormal soda has been added. The remaining 

 40 cc. must therefore have been neutralised by the ammonia obtained from the 

 nitrogenous substance investigated. This 40 cc. of decinormal acid == 4 cc. of 

 normal acid = 4cc. of normal ammonia = 4x 0.017 = 0.068 gramme of ammonia ; 

 o. 15 gramme of the substance, therefore, yields 0.068 gramme of ammonia, and 

 this amount contains 0.056 gramme of nitrogen ; 100 grammes of the substance 



investigated will therefore contain r = 37-3 grammes of nitrogen. 



(From Button's Volumetric Analysis by Warington.) 



MEASURES OF LENGTH. 



Metric System. 



The standard is the metre ; for multiples of the metre prefixes deca- hecto- 

 and kilo- are used ; for subdivisions thereof, milli- centi- and deci- are 

 used just as in the case of the gramme in the table below. 



i millimetre =0.001 metre = 0.03937 inch, 



i centimetre =0.0 1 0.3937 ,, 



i decimetre -=o.io =3.93707 inches. 



I metre -=39-37 o 79 



I inch 25. 4 millimetres. 



I foot 1 2 inches - 304. 8 



