84 CALIFORNIA ACADEMY OF SCIENCES. 



water and the filtrate evaporated to about 5 or 6 c.c, with 

 the addition of one or two drops of sodium carbonate, then 

 made acid again and added to the 10 or 15 in the graduated 

 cylinder, and the water used for rinsing the dish utilized to 

 fill up to 25 c.c. 



3d Operation. — Titration hy hypochlorite of sodium. — I 

 must suppose that the chemist who takes interest in the 

 subject treated here is acquainted or makes himself ac- 

 quainted with what Fresenius in tlie sixth edition of his 

 celebrated book remarks on titration of bromine. He will 

 find that all these titrations are based on liberating bromine 

 by chlorine and on the color imparted by free bromine to 

 water, or chloroform or other absorbent. My method offers 

 nothing new in that respect. Generally chlorine water is 

 used as standard solution, which is the most changeable 

 liquid employed in volumetric analysis. Figuier removes 

 the bromine liberated by boiling; Reimann by chloroform. 

 In the first case it requires better eyes than mine to recog- 

 nize coloring when there are only one or two milligrams of 

 bromine left, and in the second, frequent removal of the 

 chloroform is necessary; for, while the decoloration of a 

 small drop of chloroform slightly colored is a sure and deli- 

 cate test, the change of color in a highly colored drop of 

 chloroform is a ver}- coarse one. 



As standard solution I use hypochlorite of sodium or po- 

 tassium, that is, ordinary " Eau do Javelle," as prepared by 

 druggists (by treating "chloride of lime" with sodium or 

 potassium carbonate), containing, generally, from one to two 

 per cent, of chlorine, which may be set free by an acid. 

 The slight excess of the carbonate employed does not 

 interfere. I dilute one part of the commercial liquid with five 

 parts of water, and test its strength by a normal solution of 

 potassium bromide, acidulated by sulj)huric acid. This 

 normal solution I prepare by dissolving 1 grm. potassium 

 bromide in water, add diluted sulphuric acid containing 

 about 2 grm. SO3 and fill up with water to say one-half liter. 



