Abstract
Adams 1 stated that the interferometer was a precision instrument suitable for all sorts of determinations in which the refractometer has been used, with the additional advantage of being much less susceptible to temperature change and much more accurate. He states that with the refractometer one must regulate the change in temperature to 0.01° in order to secure an accuracy of one unit in the sixth place, but the interferometer requires no special regulation of temperature to secure an accuracy of one unit in the seventh place. In determining serum proteins, we found that a serum which read 454 at 15°, would read 452 at 30°, the difference being equivalent to 0.014% protein. Therefore, all readings have been made at room temperature.
The water interferometer is supplied with 5, 10, 20, and 40 mm. chambers. The 5 and 10 mm. chambers can be fitted with a 4 and 9 mm. insert, respectively, thus furnishing a chamber 1 mm. in depth with the advantage that it can be easily cleaned on removal of the insert. The scale of the instrument is divided into 3000 divisions or Trommelteil (T.T.), but we limit our readings to 1500 T.T., because it has been found that if the concentration of a solution is plotted against the T.T., the line becomes curved above this figure.
All interferometer chambers have to be standardized against known solutions. We used the method described by Robertson for preparing standard protein solutions, and found that a 1% solution of serum protein gave a reading in the 1 mm. chamber of 136.
Hirsch 2 described a method for determining serum proteins, and the method used by us is similar with the exception that we do not dilute the serum.
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