TM 1-1500-204-23-3 a. Water.    When  operating  aircraft  at  temperatures  below  freezing,  or  when  temperature  may  drop  below  the freezing point, open the oil tank sump drains sufficiently to drain off any accumulation of water. b. Solids.  Carbon and metallic particles are the two most common types of solid contaminants. (1) Carbon.    Frequently,  carbon  breaks  loose  from  the  interior  of  the  engine  in  large  pieces  which  have  the outward appearance of metal.  However, carbon can be distinguished from metal by placing the foreign material on a flat metal object and hitting with a hammer.  If material is carbon, it will disintegrate when struck with a hammer, whereas metal will either remain intact or change shape, depending upon its malleability. NOTE The information in the following paragraph is not intended to be a substitute for, nor release from,   the   requirement   for compliance with the Army Oil Analysis Program (AOAP) directed in accordance with TB 43-0106. (2) Metallic Particles.  Metal particles found in an engine may be of five kinds: steel, tin, aluminum, silver, and copper (or bronze).  A visual inspection as to color and hardness will occasionally be sufficient to determine the kind of metal present When visual inspection does not positively identify the metal, the kind of metal present may be determined by a few simple tests performed with a permanent magnet, electric soldering iron, and approximately 2 ounces each of hydrochloric acid and nitric acid as follows: (a)    Steel particles.  Steel particles can be isolated by means of a permanent magnet. (b)    Tin particles.  Tin particles can be identified by their low melting point.  A soldering iron should be cleaned, heated to approximately 500  °F (260  °C), and tinned with 50-50 solder (50% lead to 50% tin).  Wipe off excess solder.  A tin particle dropped on heated iron will melt and fuse with the solder.  Take care to avoid excessive overheating of iron during this test Exercise care in handling acid.  Acid can bum if splashed on skin. (c) Aluminum  particles.    Aluminum  particles  may  be  identified  by  their  respective  reaction  with  hydrochloric acid.    When  a  particle  of  aluminum  is  dropped  into  hydrochloric  acid  it  will  fizz  with  a  rapid  emission  of bubbles.  The particle will gradually disintegrate and form a black residue (aluminum chloride). (d) Silver and copper.  Silver and copper (or bronze) may be identified by their respective reactions in nitric acid.  When a silver particle is dropped into nitric acid, it will react rather slowly, producing a whitish fog in the acid.  When a particle of copper (or bronze) is dropped into nitric acid it will react rapidly, producing a bright green cloud in the acid.  There is no need in this instance to separate copper from bronze. c. Prevention.    Care  should  be  taken  in  the  servicing  and  maintenance  of  oil  systems  to  prevent  contamination. The oil tank filler cap must be installed correctly and locked in place.  Oil should be drained, inspected, and changed to ensure a dean supply of oil for the engine. d. DELETED. 3-6.  Oil System Maintenance.  Oil System types and general oil system component maintenance are explained in the following paragraphs. a. Types, Wet-sump and dry-sump oil systems are used in reciprocating and turbine engine aircraft for lubrication. (1) Reciprocating    engines.      Reciprocating  engines  use  both  wet-sump  and  dry-sump  systems  to  lubricate internal moving parts. (a) Wet-sump.  This system consists of a sump or pan in which the lubricating oil is contained.  The oil is drawn  from  the  sump  to  lubricate  the  engine  by  an  oil  pressure  pump.    After  lubricating  the  various  units  on  which  it sprays, the oil drains back into the sump and the cycle is repeated.  Figure 3-2 shows a typical wet-sump system. • The main disadvantages are:    · The oil supply is limited by the sump (oil pan) capacity. • Provisions for cooling the oil are difficult to arrange because the system is a self-contained unit. • Oil  temperatures  are  likely  to  be  higher  on  large  engines  because  the  oil  supply  is  so  dose  to  the  engine  and  is continuously subjected to the operating temperatures. Change 1  3-3