SCIENCE 



NEW YORK, SEPTEMBER 9, 1893. 



THE IMPURITY OF ICE. 



BY CHARLES PLATT. 



When we consider the large quantities of ice used annually in 

 the United States, especially during the summer months, when 

 drinking-water without ice is indeed a rarity, it seems strange 

 tliat the purity of the ice should so seldom be questioned. On 

 the contrary, while many people will exercise the greatest caution 

 regarding their drinking-water, the origin or source of their ice- 

 supply troubles them not at all. The ice-man brings it, and there 

 is no further need of investigation. This feeling of danger on the 

 one hand, and perfect security on the other, have been, without 

 doubt, due to that peculiar science, "popular chemistry," so 

 widely disseminated in various publications of tlie laud, and es- 

 pecially in the newspapers of the smaller towns with their " patent 

 imsides " bristling with various startling items, often of scientific 

 import. 



That this theory, once so popular, of the purification of water 

 by freezing is not in accordance witli facts is hardly worth demon- 

 stration; we will simply state that while water in its crystalline 

 state should theoretically be nearly pure, still, owing to its peculiar 

 formation in needle-Uke crystals, considerable foreign matter 

 present in the water in suspension may be, and is, mechanically 

 held within the mass. 



On the other hand, of late years there has been a revulsion of 

 public sentiment, and statements have been made denying that 

 water is purified at all by its crystallization. Others have gone 

 so far as to say that certain bacteria thrive besc at this low tem- 

 perature, and, whilst they may be harmlessly disseminated through 

 the ^vater, in the ice they have become concentrated and doubly 

 active. This certainly cannot be sustained by any known facts 

 regarding bacteriological growth, and yet may have some founda- 

 tion in the fact that in the freezing of still water, such as that of 

 a pond, or small lake, there is a certain concentration of some 

 species of bacteria at the surface of the water, and thus the first 

 inch of ice may contain these in increased numbers as compared 

 with a sample of water from the same lake. As to the increased 

 activity, or indeed as to any vital activity at all of these bacteria, 

 this is another question, and yet to be proven. When this ice is 

 melted, however, and the temperature of the resultant water is 

 raised maybe to the full heat of a summer's day or to that of an 

 over-heated room, then we have another problem, that of possible 

 decomposition and organic change in these organisms that may 

 induce results equal to and exceeding those of the bacteria them- 

 selves. 



We do not mean to say that all bacteria are necessarily killed 

 outright by the freezing of the water, — the contrary has been 

 proven in many cases, and notably by Dr. Prudden in his well- 

 known experiments with the germs of typhoid fever, —but, in this 

 as in other cases, the germs were found to be present always in 

 decreasing numbers, and in longer or shorter time their vitality is 

 lost altogether. Disease has undoubtedly been produced by use 

 of ice from polluted sources, and this, too, when mere analysis of 

 the ice in comparison with water standards would by no means 

 condemn it. But here let us state that we can by no means use 

 water standards in the analysis of ice. The standards must be 

 much higher, and the analysis must needs be conducted with 

 great care in order to arrive at correct results, even in cases 

 where the ice may be in a manner contaminated. 



In regard to the preparation of samples for analysis, Wm. R. 

 Nichols, in his admirable work on " Water Supply," gives a few 



simple directions that every chemist will do well to follow. "In 

 melting ice for analysis, a fair specimen cake should be selected and 

 broken into fragments in a clean place. The fragments may then 

 be placed in a wide-mouthed bottle covered with a plate of glass, 

 and when enough of the ice has melted to have washed itself, 

 this portion of the water is poured away and the remainder, after 

 melting, subjected to analysis.'' The same author points out the 

 danger of exposing the melting ice to the air, owing to its liability 

 to attract organisms from the air itself, thus vitiating entirely the 

 results of the analysis. 



In the year 1888, the State Board of Health of Massachusetts 

 was directed " to make a special investigation with reference to 

 the pollution of ponds, lakes, streams, and other bodies of water 

 used as ice supplies " in that State. The results of this investiga- 

 tion, which was admirably conducted, are of extreme value; as, 

 by the systematic methods adopted, they were enabled to secure 

 considerable data of general and vital interest to the public as 

 well as to the chemist. Fifty-eight sources of supply were ex- 

 amined, their chemist making, in all, analyses of seventy-six 

 samples of water and two hundred and thirty-six samples of ice. 

 The deductions drawn from their work, stated as concisely as 

 possible, are as follows : In the formation of the ice the color and 

 saline matter of the water is completely removed, and also all 

 but 13 per cent of the other impurities. The same cake of ice 

 will vary greatly as to quality in different parts. The substances 

 in solution are excluded from the ice in much larger proportion 

 than are those in suspension. Of the different kinds of ice, classi- 

 fied as snow ice, bubbly ice, and clear ice, the two former contain 

 a far greater percentage of impurity than the latter, while the 

 upper thii-d of the cake in all cases carries a higher percentage of 

 impurity than the lower two-thirds. 



Snow falling upon thin ice will cause it to sink, and finally the 

 snow will become saturated with water ; which, in turn freezing, 

 includes within the mass all of its impurities. Then, too, the 

 falling snow has already collected from the air such impurities 

 as were contained, and those also are to be found in the resultant 

 snow ice. The flooding of an ice-field by cutting holes and allow- 

 ing the water to spread over the ice surface, there to freeze, gives 

 a layer of ice of equal impurity with the water itself; and yet this 

 method of rapidly building up the ice-crop is practised to a great 

 extent throughout the country. 



That the bacteria are largely to be found in the surface and 

 snow ice can be seen by the following figures, arrived at by the 

 above mentioned Board of Health. In snow ice was found 81 per 

 cent as much bacteria as in the water itself. The ice as a whole 

 contained but 10 per cent, and the clear ice but 3 per cent. The 

 average results of all the analyses made by the Board of Health 

 show that the total organic impurities of snow ice amount to 69 

 per cent of those of the water, and the organic impurities of all 

 the ice except snow ice 13 per cent, while the clear ice contains 

 but 6 per cent. The color was entirely removed and the saline 

 matter nearly so. 



As mentioned above, the impurity of the snow ice is not due to 

 the water alone, but the air as well must be looked to to account 

 partly for this great increase of organic matter. 



These figures might tend to give one a feeling of great security 

 in using ice, as at first thought the decrease of organic matter in 

 clear ice from that originally present in the water itself would 

 seem to argue perfect safety in using ice from any ordinary sup- 

 ply. The Massachusetts Board of Health, however, carefully 

 point out that it is not the number of bacteria alone that is to be 

 considered, but their kind, and they insist that no water-supply 

 that is not fit for drinking purposes should for any reason be used 

 as a supply for ice ; and yet how often is this the case ; stagnant 

 ponds and even sluggish canals receiving their drainage from 



