46 Papers from the Department of Marine Biology. 



enough space is left to admit the NaOH, which is run in before the 

 flask is filled to the mark. It is usually necessary to adjust the NaOH 

 concentration by successive titrations and dilutions with freshly 

 boiled distilled water before it can be measured with sufficient accuracy. 

 All solutions should be sealed or provided with soda-lime tubes. The 

 sealed tubes of saturated NaOH gradually become contaminated by 

 the solution of glass. This process is slower in the borax solution, but 

 it should be kept in the best resistance glass available. 



Our boric acid was recrystalhzed several tunes in quartz beakers and 

 the reagent borax was titrated, to make sure of the proper Na content. 

 We standardized our HCl solution with reagent NaHCOs that had 

 been heated to 270° to 300° (short of sintering) by Dr. F. B. Kingsbury, 

 using methyl orange as indicator and a CO2 solution for standard color 

 of the end-point of the indicator. The weights used were standardized 

 and volumetric apparatus certified and used at constant temperature. 

 All of these precautions are probably not necessary, however, to 

 duplicate our results. Owing to the high concentration of the buffers 

 larger absolute errors are permissible than in Sorensen's buffer mixtures. 

 The boric acid can be titrated in borax with C02-free NaOH, using 

 phenolphthalein as indicator, provided large quantities of neutral 

 glycerol are added to prevent hydrolysis. 1 m NaOH titrates 1 m 

 H3BO3 (Tread well-Hall). We consider this titration superfluous, 

 provided the crystals do not appear to have lost water, and especially 

 if the Na content is correct. It is probably less expensive to obtain 

 pure borax than to titrate it. 



A little care is necessary in comparing the color of the tubes. If 

 parallel rays of light are passed through them they act as lenses, con- 

 centrating the light to a line and making comparison difficult. If 

 ground (sand-blasted) glass is used to disperse the light, the granular 

 appearance prevents the most exact estimation of the color. We 

 found the only satisfactory background to be a piece of very thin opal 

 glass placed close behind the tubes. The middle portions of the tubes 

 then appear uniform. In order to increase the accuracy of the observa- 

 tions, we removed the lenses from a stereoscope, placed their inner edges 

 together, and fastened them at such a distance (8.5 to 10 cm.) in front 

 of the tubes that when one eye was closed and the other held about 6 

 inches from the lenses, the centers of the tubes were brought together 

 in a sharp line. Two colorimeters of this nature were made and 

 proved satisfactory. The only serious difficulty we had was in making 

 the illumination symmetrical. This is easily done by allowing direct 

 sunlight to fall on the opal glass of the colorimeter and adjusting a 

 pair of gim-sights (that have been placed for the purpose on the top of 

 the instrument) in line toward the sun, but the eye is made unfit for 

 colorimetric work for some minutes unless a dark glass is used. Owing 



