ANALYTIC PROCESSES 27 



tin is a good material. Moerrs found that Jena- 

 glass tubes resist the action of the ammonium 

 hydroxid. Distillates should be titrated promptly 

 as alkali may be dissolved from the glass. 



A satisfactory condensing arrangement for 

 general laboratory use is a copper tank of good 

 size, through which several condensing tubes pass. 



Aldehyde Number. — The addition of formalde- 

 hyde to milk increases the acidity by an action on 

 the proteins. As commercial formaldehyde is 

 always acid, the acidity must be either determined 

 or neutralized in applying the following method. 

 The application of the reaction to determination 

 of proteins in milk is due to Steinegger. Rich- 

 mond and Miller investigated the method and 

 suggested the use of strontium hydroxid instead 

 of sodium hydroxid. Richmond gives the 

 following details: 



To 10 c.c. of milk at least i c.c. of a 0.5% 

 solution of phenolphthalein is added and the 

 liquid neutralized with standard strontium hy- 

 droxid solution. To the faintly pink liquid, 2 

 c.c. or more of 40% formaldehyde solution are 

 added and the titration made to the same tint 

 as the former. The strontium hydroxid required 

 by the formaldehyde solution must be known, 

 and this being deducted from that which |was 

 used in the titration and the remainder calculated 



