this doesn't seem to be such a good idea for the acid has decompose the sodium cyanide selfie forming a kaleido suspension of some for the reaction has also from sodium sulfite it is logical therefore that by adding a it is also desirable that the fixing bath contain something that will harden the gelatin emulsion so that it may be dried readily and so that the film when dry will not be easily scratched for this purpose potassium aluminum sulphate or al employing the effect of the alum as demonstrated by this melting point test one of the two strips of film on this wooden frame has been fixed in a plain hypo solution whereas the other has been fixed in one containing potassium al the water in the beaker is slowly heated we note that the emulsion which has not been hardened melts away from the transparent film support while the other remains attached the ingredients of salem was handled manually and the photographic quality was judged by eye after loading a rack with film it was developed in a small tank if at first it wasn't right dunk dunk or gram the only scientific apparatus used was a thermometer in the summer a little ice was added to the developer and in winter hot water was convenient after fixing and washing in similar tanks that was put up to dry and the surplus moisture was removed by wiping it with the sponge prints from the negative onto a positive film were made by exposing each little frame of picture one by one on a slow machine such as this one automatic precision control is the keynote of the modern laboratory these instruments continuous records of operating conditions such as relative humidity air and water temperature rise and generate a voltage developing solution temperature controlled within one tenth of a degree to keep adding solutions if a proper temperature was enormously for you adding machines are required for this one has a daily cooling capacity equal to two hundred fifty tons of ice even  storage of film is under controlled conditions balts is kept cool and is provided with automatic sprinklers for five prevention in a modern laboratory quality is not left to human judgment but is controlled by scientific methods for example developers are maintained by tests in the chemical laboratory by the use of special apparatus to even run and hide when their own concentration of developers may be measured and the developer kept up the strength by the of the necessary chemicals the analyst here makes a sample of the developer acid and allows ether to bubble through the sample one of the most important characteristics of processing solutions is their ph the analyst is here measuring the ph of a developer by means of a meter with a glass electrode sodium carbonate these values must be held within close limits the photographic characteristics of the films are measured by means of these film strips a series of increasing exposures are made on an instrument called a sense a timer and after processing a series of increasing densities can be seen correspond to the different tones of gray in an actual picture ranging from white to black to the degree of blackness so density is measured on a photoelectric cell since the density is very directly as a logger them of the exposures it is possible to product her which is valuable as a means of control having two little difference between the tone this one has to contrast a and it's hard showing too much difference between the tone i'm here is a picture correctly processed which shows a proper rendering of light and shade after each day's shooting the negative film exposed in the camera is delivered to the laboratory by these pictures were made with bright lights undeveloped film is actually handled on the damn site slides in a modern laboratory film is handled in a continuous strand passing over rollers in order to visualize how the film travels to a developing machine imagine this apparatus completely submerged in a developing solution and here we see film actively being developed in the continuous machine the film is traveling at approximately one hundred feet a minute the developer is pumped through stainless steel pipes from a large circulation tank to develop is maintained in strength by replenish or added to this tank after development the film passes into the hypo compartment where the unexposed silver bromide is removed all solutions are constantly filtered through ensure timeliness and here the fixing basket is being researched collated through crop filters the surplus over from the film naturally collects in the high post solution and here it is being removed electrically the silver plates out on large stainless steel cathodes and is thereby recovered after developing and fixing the film is watched to remove the chemicals in a modern laboratory even the rush of water is filtered from a huge filter such as this the film is now dried and here we see the process negative emerging from the dark room into a current of warm dry air not the sense that the metric strips processed with it for control and here is the finished negative a permanent record of what the camera man saw but only a means to an end the next operation in the laboratory is to make a positive print from this negative the first step is to clean the negative passing it to valve it saturated with carbon tetrachloride how do you tell what printing exposure to give the positive selam this man known as a timer is estimating the correct exposure from test strips each scene in the negative is printed on a short length of positive on a machine which gives a number of different exposures varying from li to dot by examining these tests the timer is able to assign a correct printing value for each scene these values are expressed in terms of print a light since the printing machines can be adjusted to provide different light intensit here is the printer which but loses both picture and sound negative onto the positive film we have not complicated the story by a discussion of sound recording suffice it to say that a negative film of the sound is obtain simultaneously with the picture i'm here with to meet to make a composite print the row of positive threaded over the sprockets in such a manner that it comes in contact first with a picture negative and then with the sound at each point of contact light of the proper intensity exposes the negative record onto the positive hil and here are the finished prints the sound wave patterns lie between the picture i'm the left hand perforations today film is actually processed in one continuous strand spices do have to be made between rows however on a surprising machine as shown here so that the continuous process will not have to stop for this the elevator on the left stories up film like a reservoir falling when the film on free and emptying when the flow is interrupted first flies these scene show the operation of a continuous processing machine in which the positive f exposed developed fixed washed dried and inspected without interruption here it comes in momentary contact with the picture negative for the printing exposure now the photographic record of the sound is printed the films travel through these machines at a speed of one hundred seventy five feet a minute immediately after printing the exposed positive passes directly into the developer this one is a different design from the one preview shown but operates in a similar manner the operator inspects the film in the machine to make sure that the film is r properly on the rollers using a dim flashlight made safe by glass cloth which remove any water spots which may have formed during drying after drying the film is inspected by actual projection and is then ready to be shipped to an arc light shining through a lens projects the succession of tiny pictures on the screen and the finished product of hollywood is presented for your entertainment with millions of these crystals he converts these lifeless roles of motion picture film into the golden miracles of romance education entertainment