128 state; board of agriculture. 



or from different samples, if the relative strength is ascertained by 

 the method described below, which agree with each other within the 

 limits of weights and measures in the intensity of their blue pig- 

 ment. In other words, a litmus solution equivalent in blue pigment 

 to some standard may be made repeatedly from the same sample or 

 from different samples. 



At first we thought of using a solution of some dye, as methylene blue, 

 in preparing a standard, then the idea presented itself that azolitmin, 

 a chemical compound completely soluble in water, could be used as 

 a standard by which to standardize other litmus, or, if desired, may 

 be used in litmus media. The method finally decided upon is as fol- 

 lows: For a standard we sought a solution of such strength that one 

 cubic centimeter when added to one-hundred cubic centimeters of milk 

 would give a blue color to the intensity desired for litmus media, and, 

 after a number of experiments, we found that 2.5 grs. of azolitmin 

 dissolved in one-hundred centimeters of distilled water will give this 

 strength of solution. Using this as a measure, a number of samples 

 of litmus was standardized. Of each sample, a definite amount is 

 weighed out and dissolved in a definite volume of distilled water, 

 either by placing in an incubator at 37.5° C over night or by heating 

 in flowing steam for thirtv minutes. The two methods of dissolution 

 gave us the same results. The solution is left to settle, then filtered 

 and the filtrate compared in Nessler's tubes with the standard solution 

 (2.5 grs. azolitmin in 100 cc water) diluted one to five-thousand. By 

 diluting aliquot parts of the filtrate with definite volumes of water, it 

 may be made to correspond very closely to the standard. Distilled 

 water is neutral to litmus and it was found that by adding one or two 

 drops of a decinormal potassium hydrate solution to each Nessler's 

 tube, to make slightly alkaline and to bring out the blue color, dupli- 

 cate results could be obtained. Calculating from the weight of the 

 sample and the dilutions made, the number of grams required to be 

 dissolved in one hundred cubic centimeters of water to make a solution 

 equivalent in blue pigment to the standard may be determined. 



Thirteen samples of litmus were compared with azolitmin as to the 

 intensity of their blue color, giving the numbers recorded in table No. 

 I. The number of grams required to make one hundred cubic centi- 

 meters of standard solution is the basis of estimation. The solubilities 

 were also determined for comparison with each other and for ascer- 

 taining the relation existing between the solubility and the intensity 

 of the blue pigment. From each sample, a definite amount, approxi- 

 mately one gram, was weighed out and dissolved in about twenty- 

 five cubic centimeters of distilled water by standing over night in an 

 incubator at 37.5°C. The solution was decanted on a filter paper, 

 previously dried and weighed, and more distilled water was added 

 and decanted. This was repeated several times, and finally the residue 

 was transferred to the filter paper and washed with water until the 

 washings were free from blue. The filter paper containing the insolu- 

 ble residue was dried in an oven at 00° to 100° C to constant wei'ght. 

 The average result, only, of each sample is re'coi'de'd in Table I. 



