468 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



The French have been using Javel water or solutions of sodium 

 hypochlorite containing a.bout 85 to 90 grants of free chlorine 

 per liter. More dilute solutions rapidlj^ lose their strength, espe- 

 cially if left exposed to the air and light. Since there is some 

 loss even in the more concentrated solution, this must be titrated 

 from time to time to determine its exact strength. The volume 

 of this solution which is to be used naturally depends upon the 

 strength of the solution. The amount of free chlorine recom- 

 mended for use in polluted waters is 0.8 parts per million. The 

 sodium hypochlorite has the advantage of being a relatively clear 

 solution. It is, however, much more bulky than the bleaching 

 powder containing the same amount of free chlorine. In addi- 

 tion the container is likely to be broken with consequent damage 

 to any goods with which the solution may come in contact. 



The Rhein method (124) uses antiformin instead of Javel 

 water. To every liter of water 2.1 c.c. of antiformin and 1.1 c.c 

 of 25 per cent hydrochloric acid are added. (Antiformin is sim- 

 ilar to Javel water but is usually strongly alkaline with caustic 

 soda.) The acid sets free the chlorine and it may reach a con- 

 centration of 110 p.p.m. After five minutes a tablet containing 

 0.45 grams of sodium thiosulphate and 1.7 gms. of NaHCOg is 

 added. Gothe (103) has shown a number of errors in this paper, 

 but the most important fault to be found Avith the process is the 

 necessity for malting accurate measurements of powerful chemi- 

 cals. The ordinary untrained man might easily make a mistake. 



Tablets or capsules of calcium hypochlorite have been sug- 

 gested by a number of writers. All of these are open to the Cb- 

 jection that they lose chlorine and are not suitable for use after 

 a few weeks on that account even when packed in tight vials of 

 amber glass. The tablets have been made of the chemical alone 

 or in comlbination \^dth sodium carbonate, lactose and so on. The 

 density of the tablets is objectionable- — esfpecially when eomv 

 posed of the hypoclilorite alone — since they must be crushed or 

 else a considerable amount of the substance will be kept from 

 taking part in the reaction. Vincent and Gaillard (134) claim 

 that by mixing sodium chloride with the hypochlorite, crushing 

 is made unnecessary. The salt dissolves out leaving the tablet 

 so porous that all of the active chlorine escapes into the water 

 within ten minutes. The tablet designed for one liter of water 

 contains 3 to 3.5 milligrams of active chlorine. This will mean 

 that the water will receive 3 to 3.5 parts per million of free chlor- 

 ine. 



