458 



Mr. W. North. The Influence of 



free, a quality possessed by no shoulder knapsack with which I am 

 acquainted. 



The urine and fseces of the previous day were carried to the labo- 

 ratory every morning by myself, and were analysed after the follow- 

 ing methods. 



Methods of Analysis of Urine and Faces. 



The urine was passed directly into the wide-mouthed bottles already 

 described, and after the specific gravity had been taken, was poured 

 into a large measuring cylinder, and the amount noted. Distilled 

 water was then added, in order to bring the quantity to a round 

 number of cubic centimeters, e.g., if the original quantity was 1320 c.c, 

 water would be added to make it up to 1400 c.c. After the whole 

 had been thoroughly mixed, the analysis was proceeded with. 



This plan was adopted to avoid the risk of arithmetical errors in 

 the subsequent calculation of the results of the analyses. 



Nitrogen. — This was estimated by combustion with soda-lime, after 

 the Munich method. 10 c.c. of urine were taken and evaporated 

 with a small quantity of well-burned Calais sand and a trace of oxalic 

 acid, over a water-bath at the boiling temperature, in exceedingly 

 thin hemispherical glass dishes. When thoroughly dry the dish and 

 its contents were pulverised in a mortar — all precautions being taken 

 to prevent loss — mixed with soda-lime, and the analysis proceeded with 

 in the usual way. The estimations were made by titration with 

 cochineal as indicator. 



Instead of glass tubes I have used Wrought-iron ones, carefully 

 tested under hydraulic pressure up to 300 lbs. on the inch. 



Objection has been made to the use of iron tubes, on the ground 

 that when hot there is a danger of their leaking, and that the corks 

 burn. I have found these difficulties to be more imaginary than real, 

 and with a little practice and the use of ordinary care I have obtained 

 the most excellent results. Recently I have made a number of experi- 

 ments, in which the urine, instead of being evaporated with oxalic 

 acid as above described, was introduced directly by means of a pipette 

 into a tube already charged with 2 or 3 inches of soda-lime, and a 

 small quantity of cane-sugar at the end. This latter method ulti- 

 mately proved equally satisfactory with the former, but it requires 

 great caution and careful watching during the process of heating, to 

 prevent the sudden development of steam in quantity sufficient to blow 

 the acid out of the bulbs ; but this accident can be avoided without 

 very great difficulty. I have found it desirable, particularly when 

 the latter method is used, to employ bulbs considerably larger than 

 those generally sold for the purpose, and to have a small additional 

 bulb blown, from which the point takes its origin. This is a great 

 safeguard against the effects of possible splashing. 



