JFaters of the Dee and Don at Aberdeen. 313 



III. — Action of Clark's Soap- Test on Dee Water. 



In many trials of Dee water, taken either directly from 

 the river, or from the laboratory pipe, the hardness was found 

 to vary between 1°-1 or l°-2, and l°-75. But different trials 

 of the same specimens have sometimes varied a little — such 

 a variation as I have been accustomed to find in solutions of 

 very low degrees of hardness, especially when this hardness 

 is caused partly by magnesia. In specimen A, the hardness 

 varied in three trials from 1°-1 to 1°*14. After standing a 

 day or two, the lathers could not be renewed without a 

 further addition of soap-test, raising the hardness thus in 

 two of the cases to l°-36. Taking the mean between the 

 highest and lowest, we may assume the hardness of specimen 

 A to be l°-23 ; and this agrees accurately with three trials 

 made on water drawn from the laboratory pipe on the 28th 

 of September, which should not have differed much from 

 river water of the 24th. The greatest hardness observed 

 was in specimen B, taken direct from the river on the 15th 

 of February. It turned out l°-75 ; but as the specimen was 

 highly aerated, it is just possible that a little of this apparent 

 hardness may have arisen from carbonic acid. 



In specimen A, I distinguished the hardness caused by 

 lime from that caused by magnesia, by means of the soap- 

 test, as follows : A mixture of equal bulks of standard 

 lime solution 20° and distilled water was tried, and the 

 hardness noted. A similar mixture of same solution 20° 

 and specimen A was then made, and the hardness deter- 

 mined. The difference was O^'^T. This, multiplied by 2 

 (as the Dee water operated on was only half the standard 

 quantity), gives 0°-94, the hardness caused by lime ; and 

 subtracting this from 1-23, the total hardness, leaves 0°-29 

 as the hardness resulting from magnesia. By an extended 

 course of experiments, I had previously satisfied myself that 

 the soap-test is not affected by any quantity of magnesia 

 under 6° or 8°, if associated with at least 10° of lime ; hence 

 the contrivance of the above experiments. If the whole 

 lime in the water, as given in the preceding analysis, page 

 125 (omitting what may exist in the precipitate by ammonia) 

 be calculated as carbonate, the amount will coiTespond 



