434 



NA TURE 



{March 30, 1876 



machine, manufacturing 250 kilogrammes of ice per 

 hour : — 



A cylindrical tubular copper boiler has a length of 

 2 metres and a diameter of 35 centimetres ; 150 tubes of 

 15 millimetres traverse its entire length, and are soldered 

 by their extremities to the two ends. This first boiler is 

 the refrigerator. It is placed horizontally in a large 

 sheet-iron vat, which contains 100 tanks of 20 litres each. 

 An incongealable liquid, salted water, is constantly circu- 

 lating in the interior of the refrigerator by means of a 

 helix. This liquid is re-cooled to about — 7° in a normal 

 course, and it licks on its return the sides of the tanks 

 which contain the water to be frozen. 



In the space reserved between the tubes of the refri- 

 gerator, the sulphurous acid liquid is volatilised, its 

 vapours are drawn up by an aspirating force-pump, which 

 compresses them without the condenser. This condenser 

 is a tubular boiler, the same as the refrigerator ; only a 

 current of ordinary water passes constantly into the inte- 

 rior of the tubes to carry off the heat produced by the 

 change of the gaseous into the liquid state of the sul- 

 phurous acid, and by the work of compression. A tube 

 furnished with a gauge tap, adjusted by the hand once 

 for all, permits the liquefied sulphurous acid to return 

 into the refrigerator to be subjected anew to volatiUsa- 

 tion. 



Sulphurous acid has the exceptionally advantageous 

 property of being an excellent lubricant, so that the 

 metallic piston which works in the cylinder of the com- 

 pressing pump requires no greasing. Thus the introduc- 

 tion of foreign matter into the apparatus becomes entirely 

 impossible. 



The work necessary to manufacture 250 kilogrammes 

 of ice per hour is at the most seven-horse power. 



A cold of 7° in the bath is amply sufficient to obtain in 

 the tanks a rapid and in every way economical conge- 

 lation. 



With these mechanical arrangements the following im- 

 portant advantages are realised :— i. The pressure never 

 exceeds four atmospheres. 2. There is never any entry 

 of air to fear, the pressures, as far as — 10° C, being 

 always above that of the atmosphere. 3. The volatile 

 liquid employed is perfectly stable, undecomposable, and 

 without chemical action on metals. 4. All greasing in 

 the machine is dispensed with. 5. The volatile liquid is 

 obtained at a very low price, and it is accompanied by no 

 danger of explosion or fire. 6. The cost of production of 

 the ice approaches infinitely near to the theoretic mini- 

 mum : it is about 10 francs per ton of ice. 



By means of all these advantages the practical problem 

 of the manufacture of ice may be considered as solved for 

 all climates, and the process of M. Pictet will not fail to 

 be speedily adopted in all warm countries as soon as it 

 becomes known ; it is in such countries that its happy 

 results will be specially utilised and appreciated. 



A small specimen of M. Pictet's machine will be shown 

 at the forthcoming Loan Exhibition of Scientific Apparatus 

 at South Kensington. 



APPARATUS FOR DEMONSTRATING THE 

 TRANSFORMA TION OF FORCE 



IN a recent number of the Journal de Physique^ M. 

 Crova describes a convenient apparatus for showing 

 the relations between heat, electricity, and mechanical 

 force. The arrangement is as follows : — 



Two of Clamond's thermo-electric generators are con- 

 nected in surface, and put in communication with a 

 Gramme machine in such a way as to set this in action. 

 In the circuit is inserted a sort of electric lamp, in which 

 a platinum wire placed in the centre of a small globe 

 (which protects it from agitation of the air) can be raised 

 to incandescence. The only difficulty of the experiment 

 consists in so regulating the length and diameter of the 



platinum wire as that it may be raised to a red heat, 

 while the thermo-electric current retains sufficient inten- 

 sity to drive the Gramme machine. A circuit entirely 

 metallic then is obtained, with which the following trans- 

 formations can be effected : — 



1. The Gramme machine being excluded from the 

 circuit, a portion of heat, transformed into electricity by 

 the thermo-electric pile, reappears in the state of heat in 

 the platinum wire. 



2. The platinum wire being excluded from the circuit, 

 and the Gramme machine introduced, a portion of heat, 

 transformed into electricity in the pile, produces mechanical 

 work in the machine, which acts as a motor. 



3. The platinum wire and the machine being included 

 in the circuit, a part of heat, transformed in the pile into 

 electricity, produces heat in the wire and work in the 

 motor. If we then stop the motion of the Gramme ma- 

 chine, we find the incandescence of the platinum wire 

 increased. The machine being liberated, on the other 

 hand, is set agoing again, and the incandescence of the 

 platinum wire diminishes in proportion as the motion is 

 accelerated. In this way is rendered sensible to the 

 eye the expenditure of heat necessary to develop an 

 increasing quantity of mechanical work. 



4. Taking the handle of the machine, we turn it in the 

 direction of the rotation the current produces, but with an 

 increasing velocity. In this way a velocity is reached 

 such that the incandescence of the wire completely dis- 

 appears. 



5. If the handle be turned in a direction opposite to that 

 of the rotation the current communicates, there is con- 

 siderable resistance, and the incandescence of the wirs 

 increases rapidly ; on turning more quickly, the wire is 

 fused. Thus, in the metallic circuit under consideration, 

 the circulation of a given quantity of energy may appear 

 exteriorly in the form of heat or of mechanical work, the 

 one of these quantities being the complement of the other. 

 If by an exterior force we introduce into the circuit an 

 additional quantity of work, the increase of the quantity 

 of energy put m circulation is rendered visible by the 

 incandescence of the wire ; any communication outwards 

 from the circuit, of a certain quantity of energy which 

 circulates in it, appears, on the other hand, in diminution, 

 or even disappearance, of the incandescence. 



NOTES 



Lord Salisbury, on Monday, named the following as Com- 

 missioners under the Oxford University Bill : — Lord Selborne 

 (Chairman), I-ord Redesdale, the Dean of Chichester, Mr, 

 Mountague Bernard, Sir Henry Maine, Mr. Matthew White 

 Ridley, and Mr. Justice Grove. The feeling among scientific 

 men is one of intense disappointment, leading to the conclusion 

 that it is useless any longer to consider whether Oxford will ever 

 be in a position to do anything for the promotion of science. 



The report of the Cambridge Board of Mathematical Studies 

 to the Studies' Syndicate contrasts with the reports of most of 

 the other boards in the paucity of its suggestions for improve- 

 ment. They do not seem to think that very much is required in 

 order to perfect the system of mathematical teaching. They 

 believe in the probable stability and development of the system 

 of inter-collegiate lectures, but say very. little to assist its deve- 

 lopment, and they say nothmg about the present vehement com- 

 petition by means of private tuition, and the defective method 

 of study that it induces. In answer to the question how Uni- 

 versity teaching may be organised so as to give the greatest 

 encouragement to the advancement of knowledge, " the Board 

 offer no suggestions under this head." Is this quite what might 

 have been expected in a report bearing the signatures of Stokes, 

 Cayley, Adams, Clerk-Maxwell, Sir W. Thomson^ Tait, Lord 



