



Intro, fig. 94. Kemmerer water sampler. Note metal 

 messenger at top of photo. 



Dissolved oxygen determination. — 1) To the sample 

 collected in the 250-300 cc. ground-glass stoppered 

 bottle, add 1 cc. of manganous sulfate and 3 cc. of 

 alkaline potassium iodide beneath the surface of 

 the liquid. 2) Replace the stopper, at the same time 

 preventing the entrapping of air bubbles. Shake vigor- 

 ously for fifteen seconds and allow the precipitate to 

 settle until it is contained in the bottom half of the 

 bottle. If this does not occur quite rapidly the shaking 

 should be repeated. 3) When the precipitate has 

 settled, add 2 cc. of concentrated sulfuric acid above 

 the water level, holding the tip of the pipette against 

 the neck of the bottle. Replace the stopper with pre- 

 cautions against trapping air bubbles and shake the 

 bottle vigorously to mix the contents. Up to this 



65 

 Lattin: Introduction 



point tho procedure must be carried out in the field. 

 The final titration should be made as soon as possible 

 thereafter, but an elapse of a few hours is permissible. 

 4) Transfer 200 cc. of the treated sample, measured 

 with a 200 ml. volumetric flask, into a 500 cc. Erlen- 

 meyer flask. This is conveniently accomplished b\ 

 carrying into the field a 200 cc. flask cut off a few 

 millimeters above tho mark and inserted into a pierced 

 stopper which fits the neck of the larger flask. By 

 inserting the mouth of the smaller flask into the 

 larger flask and reversing tho two with a slight rotary 

 motion the sample will transfer rapidly. 5) Titrate the 

 sample with 0.025 N sodium thiosulfate. One or two 

 cc. of starch solution should be added only when the 

 color has become a faint yellow after the addition of 

 thiosulfate. Titrate over a white background until 

 the blue color disappears. Dissolved oxygen is 

 reported in parts per million by weight. If a 200 cc. 

 sample is used the dissolved oxygen in parts per 

 million is equal to the number of cc. of .0.025 N thio- 

 sulfate required. No corrections are necessary except 

 for work of unusual precision. Since the 0.025 N 

 solution of thiosulfate is unstable, this solution 

 should be restandardized or replaced occasionally. 

 Starch solutions, even if preservatives such as 

 chloroform or zinc chloride are added, deteriorate 

 quite rapidly, especially in warm weather. A satis- 

 factory method is to use sterilized solutions in small 

 bottles which are opened as required. 



Carbon dioxide determination. — Collect 100 cc. of 

 the sample in a low-form Nessler tube (200 x 32 mm.) 

 according to one of the methods mentioned above. 

 Add 10 drops of phenolphthalein and titrate rapidly 

 with N/44 sodium hydroxide until a faint but perma- 

 nent pink is produced (3 minutes). The sample may 

 be mixed by swinging with a circular motion of the 

 wrist. Any agitation of the surface of the liquid tends 

 to change the gaseous content and should therefore 

 be avoided. The free carbon dioxide is equal to ten 

 times the number of cubic centimeters of N/44 sodium 

 hydroxide used. Since N/44 hydroxide or stronger 

 solutions deteriorate once the bottle is opened, this 

 solution should be restandardized, or a fresh one 

 obtained at frequent intervals. It is convenient to 

 have this reagent supplied in small, tightly corked 

 containers. 



Alkalinity. — The alkalinity of natural waters repre- 

 sents its content of carbonates, bicarbonates, hydrox- 

 ides, and occasionally borates, silicates, and 

 phosphates. It is determined by titration with a 

 standard solution of strong acid to certain datum 

 points or hydrogen-ion concentrations. Indicators are 

 selected which show definite color changes at these 

 points. Since dilute bicarbonate solutions have a 

 hydrogen-ion concentration of about pH 8.0 and dilute 

 carbonic acid solutions a hydrogen-ion concentration 

 of about pH 4.0, these are chosen as datum points, 

 and indicators should be selected which show definite 

 color changes at about these two points. The amount 

 of standard acid required to bring the water to the 

 first point measures the hydroxides plus one-half the 

 normal carbonates (phenolphthalein), and the amount 

 to bring it to the second point corresponds to the 



