"Ribonuclease II. Accuracy of measurement and shrinkage."

Date:
1954-1955
Reference:
PP/CRI/H/1/32
Catalogue details

Licence: In copyright

Credit: "Ribonuclease II. Accuracy of measurement and shrinkage.". Source: Wellcome Collection.

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    method (T.C. Furnas, unpublished). The b axis (and therefore the capil lary axis) is adjusted by means of the Eulerian cradle to be horizontal^ and the intensity of an OkO reflection (usually 020) is measured as the capillary is rotated about this horizontal axis. The paths of the X- rays can thus be made very similar to, though not quite identical with, the paths at the various angular settings used while measuring the hO^'s. From the variations in the intensity of the chosen OkO reflection, the relative absorption factor is thus found. This factor^in the best cases,varies only from 1.0 to 1.4, but a variation of 1.0 to 2.0 is not uncommon. It is therefore important not to omit it. ^Rep ^d^uci M£^^_o f_in tens^iti^es We report first the comparison between sets of hO^ intensities for two crystals which we should expect to be identical. They were both grown using a solvent containing 50°/o by volume of tertiary butyl al cohol. Their volumes were in the ratio of about 1 to 2, and their capil lary absorption corrections were 1.0 fco 1.5 and 1.0 to 2.1 respectively. Their cell dimensions were the same within the experimental error. The measured relative intensities were put on the same basis by- adjusting the scale factor so that the sum of all the intensities measured (hO-É's out to 29=30°) was the same in each case. In addition, the intensities were summed in groups, each having a small range of 1/d, and the ratio of these sums for the two sets was plotted against \ / \ |) l/d$ as s hown—dm (Fig. ij. The fact that these ratios show no systematic deviation from unity means that the 'temperature factors' for the two crystals were essentially the same. We next obtained a measure of the percentage difference in the in tensities as follows: Let I be the value of the intensity of a given