48 Papers from the Department of Marine Biology. 



It is very difficult to completely prevent the concentration of the 

 indicator solutions by evaporation while in actual use, and we did not 

 attempt to do it. We kept the solutions in small Erlenmeyer flasks, 

 each having a pipette, graduated in hundredths of a cubic centimeter, 

 passed through the stopper into the solution. Perhaps the most 

 convenient way of correcting the concentration of these solutions is to 

 make up one tube of distilled water containing the same concentration 

 of the indicator as the standard buffer mixtures, at the time the 

 standard tubes are made. There is enough CO2 in distilled water to 

 turn these indicators to their maximum yellow color, yet not enough 

 to carry them near their secondary color range (red in strong acid). 

 The yellow color is constant over a very wide Ph range. It is then 

 only necessary to determine the quantity of indicator solution neces- 

 sary to color distilled water to the same degree of yellow as the sealed 

 distilled-water tube, in order to have the amount necessary to put in 

 the same volume of sea- water in determining the Ph. Even without 

 this special tube, it is possible to determine colorimetrically (by 

 repeated trials) the amount of indicator to add to sea-water; the color of 

 each standard tube is the resultant of two colors (red and yellow or blue 

 and yellow) . It is impossible to match it with these colors in any other 

 proportion, no matter how the concentration is changed. If the proper 

 concentration of indicator is unknown, it may be found by repeated 

 trials to match the color, using sea-water of any Pg within the range of 

 the tubes. It was this consideration which led us to discard phenol- 

 phthalein and a-naphtholphthalein, since each showed only one color. 



NEW APPARATUS FOR ELECTROMETRIC DETERMINATION OF 

 HYDROGEN-ION CONCENTRATION AND FOR GAS ANALYSIS. 



TECHNIQUE OF THE EXPERIMENTS. 



The hydrogen electrodes were each made of a gold disk (later covered 

 with a thin layer of palladium black) welded to a platinum wire sealed 

 through the glass. There seems to be only one way to do this. A bit 

 of gold is wound or folded over the end of the platinum wire and held 

 in the flame until it just melts; then it is instantly removed. The 

 congealed gold drop is then hammered on to the edge of the gold disk. 

 The electrode is cleaned by filling the glass parts with a saturated 

 solution of potassium bichromate in concentrated sulphuric acid 

 (cleaning fluid) and rinsed thoroughly. 



The palladizing solution is made by dissolving about 1 per cent of 

 palladium chloride in distilled water and filtering. No reducing agent, 

 such as basic lead acetate, is necessary. In fact, our solutions were 

 weakened by spontaneous reduction, becoming dark with colloidal 

 palladium; but this finally settled out, by further reduction, and the 

 necessity of refiltering in order to watch the palladization was avoided. 



