a 
JUSTUS VON LIEBIG. 259 
* the countless white precipitates each has something peculiar to itself; 
and when one has experience in this sortof appearances, whatever one 
sees during an investigation at once awakens the remembrance of what 
one has seen. The following example will make clear what I mean by 
sight or eye memory. During our joint research on uric acid, Wéhler 
one day sent me a crystalline body which he had obtained by the action 
of peroxide of lead upon this acid. I immediately thereupon wrote to 
him with great joy, and, without having analyzed the body, that it was 
allantoin. Seven years before I had had this body in my hands; it had 
been sent to me by C. Gmelin for investigation, and I had published 
an analysis of it in Poggendorff’s Annalen; since that time I had not 
seen it again. But when we had analyzed the substance obtained from 
uric acid there appeared a difference in the amount of carbon, the new 
body gave 14 per cent carbon less, and since the nitrogen had been 
determined by the qualitative method a corresponding quantity (4 per 
cent) of nitrogen more; consequently it could not possibly be allantoin. 
However, [trusted my eye memory more than my analysis, and was 
quite sure that it was allantoin, and the thing now to be done was to 
find the remains of the substance previously analyzed in order to 
analyze it afresh. I could describe the little glass in which it was with 
such precision that my assistant at last succeeded in picking it out from 
amongst a couple of thousand other preparations. It looked exactly 
like our new body, except that examination under the lens showed that 
Gmelin, in the preparation of his allantoin, had purified it with animal 
charcoal, some of which having passed through the paper in the filtra- 
tion had become mixed with the crystals. 
Without the complete conviction which I had that the two bodies 
were identical, the allantoin produced artificially from uric acid would 
undoubtedly have been regarded as a new body, and would have been 
designated by a new name, and one of the most interesting relations 
of uric acid to one of the constituents of the urine of the foetus of 
the cow would perhaps have remained for a long time unobserved. 
In this manner it came to pass that everything I saw remained inten- 
tionally or unintentionally fixed in my memory with equal photographic 
fidelity. At a neighboring soap boiler’s I saw the process of boiling 
soap, and learned what *‘ curd soap” and “fitting” are, and how white 
soap is made; and I had no little pleasure when I succeeded in showing 
a piece of soap of my own making, perfumed with oil of turpentine. 
In the workshop of the tanner and dyer, the smith and brass founder, 
I was at home and ready to do any hand’s turn. 
In the market at Darmstadt I watched how a peripatetic dealer in 
odds and ends made fulminating silver for his pea-crackers. Lobserved 
the red vapors which were formed when he dissolved his silver, and 
that he added to it nitric acid; and then a liquid which smelled of 
brandy, and with which he cleaned dirty coat collars for the people. 
With this bent of mind it is easy to understand that my position at 
