XI. INSTRUCTION. 979 



cattle, sheep, and pigs, The plan is that of Professor M. Pettenkofer. of 

 Munich, excepting that for the aspiration of the air, which is the same as 

 that adopted in a smaller apparatus by Professor C. Voit, of Munich. .The 

 parts are as follows : 



A, chamber for the reception of the animal during the experiment. 



B, tube of tin, for the passage of the gaseous products from the chamber. 



C, a vessel in which the gaseous products are saturated with watery 

 vapour. 



D, a gasometer in which the volume of the gases is determined. 



E, tube through which the measured -ascs escape. 



F, engine (hot air) which, by turning the revolving drum of the gasometer, 

 aspirates the gases through the parts A, D, and, as a consequence, draws fresh 

 air in through the openings in the back of A'. 



To ascertain the quantities of carbonic acid, aqueous vapour, and methair 

 (marsh gas) evolved by the animal, the composition both of the gases 

 passing from the chamber A through the tube B and of the fresh air is 

 determined, with regard to their contents of these substances, and the difference 

 shows the quantities of the gases evolved. 



For these examinations the apparatus shown on the table G is employed. 

 Aspirating and forcing pumps (e, c, c,) which close with mercury, draw small 

 quantities either of air from B through the tubes a, a,... or of fresh air through 

 the tubes b, 6,... and force them through the absorption apparatus d, d,,., 

 and dl, dl, or d2, d2, to the gasometers e, e, e,... where they are measured. 



The motion of the pumps is effected by the engine F by means of the 

 mechanism o, p, q, r, s. To every absorption apparatus there appertain 

 two pumps which alternately aspirate and force, and four valves with mercury 

 joints (/,/,/...). 



The carbonic acid is absorbed by a test solution of baryta in the tubes d, d, 

 ...anddl, dl.... 



The aqueous vapour is determined in the flasks d2, d2,... which contain 

 pumice stone saturated with sulphuric acid. 



The carburetted hydrogen is oxidated by passing over ignited oxide of 

 copper. For this purpose a portion of the air to be analysed is drawn by 

 the pumps through the tubes g, g, filled with oxide of copper, and placed upon 

 a furnace H. The products of the oxidation, carbonic acid and water, are- 

 then conveyed to the absorption apparatus and gasometers. 



The drawing IV. represents a similar apparatus, but of smaller dimensions, 

 which also is employed at the I. R. Chemico-Agricultural Experruental Insti- 

 tution at Vienna. Its construction is in the main the same, excepting that 

 the ventilation is effected by the exhausting fanner K. The motion of K 

 and of the pumps (c, c,) is effected by the mechanism L, which is worked 

 either by a man or by a small water -wheel. (The other signs on this drawing 

 IV. correspond Avith those of the drawings L, II., III.) 



The smaller apparatus is used for experiments with . poultry, rabbits, and . 

 other small animals. 



3822. Photographs of Microscopic Objects. Enlarged 

 from negatives by Dr. Mocldox, for illustration by means of the 

 lantern. James How Co. 



3823. Mounted Preparation to show a method of putting 

 up drfed membranous specimens for museums. 



Prof. Strtcthers. 



The glass jar is not essential. The wire loop displays and also protects 

 the preparation, and the tube enables it to be turned round on the stand, 



3 Q 2 



