410 PHYSIOLOGICAL CHEMISTRY 



Very little is known positively regarding the actual course of the 

 excretion of the calcium under pathological conditions. An excess 

 is found in some diseases of the bones, e.g., osteomalacia. In others 

 as in rickets the urinary excretion may be very low. 



The daily excretion of magnesium by way of the urine usually 

 amounts to between o.i and 0.3 gram, expressed as MgO. The amount 

 depends mainly on the diet. About 50 per cent or more of the excreted 

 magnesium is usually eliminated by the kidneys, the remainder passes 

 out in the feces. There may be a retention of magnesium in certain 

 bone disorders accompanying a loss of calcium; in osteomalacia for 

 example. Thus the excretion of calcium and magnesium do not neces- 

 sarily run parallel. 



Carbonates 



Carbonates generally occur in small amount in the urine of man 

 and carnivora under normal conditions, whereas much larger quanti- 

 ties are ordinarily present in the urine of herbivora. The alkaline 

 reaction of the urine of herbivora is dependable in great measure upon 

 the presence of carbonates. In general a urine containing carbonates 

 in appreciable amount is turbid when passed or becomes so shortly 

 after. These bodies ordinarily occur as alkali or alkaline earth com- 

 pounds and the turbid character of urine containing them is usually 

 due principally to the latter class of substances. The carbonates of 

 the alkaline earths are often found in amorphous urinary sediments. 



Iron 



Iron is present in small amount in normal urine. It probably occurs 

 partly in inorganic and partly in organic combination. The iron con- 

 tained in urinary pigments or chromogens is in organic combination. 

 According to different investigators the iron content of normal urine will 

 probably not average more than 1-5 mg. per day. After splenectomy 

 there is an increased loss of iron from the body particularly by way of 

 the feces (Asher). 



EXPERIMENT 



Detection of Iron in Urine. Evaporate a convenient volume (10-15 c.c.) of 

 urine to dryness. Incinerate and dissolve the residue in a few drops of iron-free 

 hydrochloric acid and dilute the acid solution with 5 c.c. of water. Divide the 

 acid solution into two parts and make the following tests: (a) To the first part add 

 a solution of ammonium thiocyanate; a red color indicates the presence of iron. 

 (b) To the second part of the solution add a little potassium ferrocyanide solution; 

 a precipitate of Prussian blue forms upon standing. 



