OH. XV] EXPERIMENTS. 301 



(If (c =jSTaCl and y = KC1, 



sc + y = a (weight of residue), 



Cl Cl 



x + i y = & (weight of chlorine in a) : 



T 



from these equations the values of x and y can be found.) 



Calcium oxalate. 



Calcium oxalate can readily be estimated in plant 

 tissues by extracting a weighed portion of tissue with 

 dilute HC1, evaporating the extract to dryness and strongly 

 igniting the residue. The ignited residue is dissolved in 

 HC1 and the calcium estimated volumetrically by the 

 usual process, with oxalate and standard potassium per- 

 manganate. 



The calcium found is calculated to calcium oxalate 



(CaC A or CaC A + H a O). 



See Sutton, Volumetric Analysis, p. 133. 



Experiments on organic acids. 



(1) Compare the acidity of juice pressed out of equal 

 weights of petioles of young and old leaves of rhubarb 

 (Rheum rhaponticum). 



(2) Compare the acidity and amounts of sugars in 

 juice from ripe and unripe apples. 



Determine the acidity of the juices with r baryta and 



phenolpthalein as directed on p. 297. 



To determine the sugars take 50 c.c. of filtered and 

 diluted juice, add lead acetate as long as it causes a pre- 

 cipitate, filter and remove excess of lead by H 2 S etc. and 

 determine the sugars as directed on p. 285. 



