On the Substitution of Turbidimetry for Nephelometry in Certain Biochemical Methods of Analysis

Within the past decade nephelometric methods of analysis have become increasingly popular in biochemical work, so that at present a nephelometer has come to be counted an indispensable piece of apparatus in every well equipped laboratory. Nephelometry has however the serious disadvantage that, as was first pointed out by Richards and Wells,i the amount of light reflected is not strictly proportional to the weight of the precipitate under observation, but seems to be influenced by a variety of factors. To overcome this defect Richards and Wells adjusted the volume of their solutions so. that standard and unknown contained about the same concentration. Kobe? has suggested a mathematical formula by means of which he has obtained excellent results, and Bloor3 recommends that a standard be selected which is of such strength that it varies not more than 25 per cent from the unknown. During the past 5 years the author has had occasion, in connection with studies on blood and milk, to make extensive use of nephelometric methods, and as a result of this experience has come to appreciate more clearly the relatively large error which may be introduced in an analysis unless the strength of the standard and of the unknown are adjusted to within at least 10 per cent, a requirement which means that for a single determination it may be necessary to provide from three to six stan-