THE IMPORTANCE OF "IMPURITIES" AND TRACE SUBSTANCES 65 



at a profit, and he hoped to reduce his cost by duplicating the red 

 paste himself. Asked whether it was ideal for the purpose, he 

 admitted it had many deficiencies, but it was the best thing he 

 had found. He was then asked to write out the properties which 

 an ideal color paste should have for his purposes, and was told 

 that instead of trying to duplicate an inferior product, it would 

 be wiser to try to evolve a product as near the ideal as possible. 

 Actually, a superior color material was produced at a raw material 

 cost of nine cents a pound, and this was adapted for use on auto- 

 matic machinery which could be hired to turn out a completed 

 cosmetic. The cost of the final product, with very small invest- 

 ment, was less than 10 per cent of the original cost. 



The actual analytical work in this case contributed but little to 

 its successful conclusion. But in many, if not most cases involving 

 biological questions, very delicate and ingenious analysis lies at 

 the very foundation of the solution of a problem. The presence 

 of small traces of substances may make or mar a product, process, 

 or organism, and exact means must be found for determining 

 them. When students are criticized for not finding, say, one half 

 of one per cent of some element present in an "unknown," they 

 are prone to consider their instructors very exacting and "mean." 

 Even students with a 90 per cent average must be brought to 

 realize that in business or professional life they are expected to be 

 100 per cent right, every day. Severe penalties await the food 

 manufacturer whose product contains more than the permissible 

 few parts per million of lead, arsenic, copper, etc.; and the lives of 

 patients often depend on proper and correct reports from the 

 laboratory. 



The necessity of determining minute percentages has led to 

 ever-increasing refinements in analysis, and physical means are 

 being increasingly called upon to reinforce or to replace gravi- 

 metric and volumetric analytical methods. 



Nephthelometry, which depends on measuring, often with the 

 "electric eye" or photoelectric cell, the amount of cloudiness produced 

 in a solution by appropriate reagents, can determine, e.g., one part of 

 phosphorus in 333 million parts of water. 1 The quartz spectrograph 

 is used to determine trace impurities which may ruin a metal for cer- 

 tain purposes. Thus Colin J. Smithells states: 2 "The solubility of 

 bismuth in copper is less than 0.002 per cent, and any excess forms 

 brittle films between the copper grains. For most purposes 0.005 per 

 cent of bismuth is the maximum permissible, and where the metal is 



