Overview:
This 1916 guide, written by W.A. Shenstone, F.R.S., provides a thorough introduction to glassblowing and working with vitreous silica for chemical and physical students. The book emphasizes the importance of acquiring practical skills, saving laboratory expenses, and avoiding delays by making one’s own equipment.
Shenstone begins with a detailed description of essential tools, including various blowpipes and bellows. He explains the characteristics and management of different types of glass: soft soda glass, lead glass, and hard glass. He then carefully outlines fundamental glassblowing operations, such as cutting, bending, sealing, and widening tubes, as well as the construction of basic apparatus like bulbs and stoppers. A dedicated chapter covers the relatively new technique of working with vitreous silica, showcasing its remarkable properties and the procedures for making tubes, flasks, and other essential laboratory equipment.
Key Findings:
- The use of vitreous silica offers advantages over traditional glass for certain laboratory applications. Its high melting point, low expansion coefficient, and resistance to sudden temperature changes make it ideal for high-temperature experiments and handling.
- Careful annealing is crucial for preventing fractures in glass and silica apparatus, especially when working with thick or unevenly distributed glass. The book emphasizes the importance of slow cooling and recommends wrapping hot glass in cotton wool.
- Cleanliness is paramount when working with silica. Even small amounts of foreign matter can affect the material’s properties and lead to unwanted devitrification.
Learning:
- Glassblowing techniques: The book provides detailed instructions on various glassblowing operations, including cutting, bending, sealing, joining tubes, and blowing bulbs. This hands-on knowledge equips readers with the skills to create custom laboratory equipment.
- Working with vitreous silica: The guide introduces the properties and advantages of vitreous silica, allowing readers to explore its potential for research. It details the procedures for preparing non-splintering silica from Brazil Pebble, making tubes and bulbs, and building more complex apparatus.
- Annealing: The reader will learn the importance of annealing for minimizing stress and preventing fractures in glass and silica apparatus, as well as different methods for effectively annealing.
- Handling and care of materials: The text emphasizes the importance of proper handling techniques and cleanliness for both glass and silica. It highlights the potential risks of using the materials improperly and provides guidance on preventing damage.
Historical Context:
- The guide was written in 1916, during a period of significant advancement in scientific research. The development of new materials like vitreous silica was transforming the possibilities of laboratory experimentation.
- The book reflects the growing demand for custom-made scientific equipment, especially in remote laboratories. The author emphasizes the value of glassblowing skills for both cost-saving and efficiency.
Facts:
- Glass is composed of silica (SiO2) and metallic oxides. This composition gives glass its specific properties like melting point, viscosity, and resistance to various chemicals.
- True glass requires at least two metallic oxides for stability and fusibility. The presence of multiple oxides makes the glass more workable and less prone to devitrification.
- Lead glass is also known as English glass. It is often used for scientific apparatus because it is more resistant to cracking and sudden temperature changes compared to soda glass.
- Soda glass, also known as French glass, is less expensive than lead glass but more susceptible to cracking. It requires careful annealing to prevent breakage during cooling.
- Hard glass, used for high-temperature applications, is difficult to soften and can devitrify easily. Jena combustion tube is a preferred type of hard glass for such purposes.
- The pointed flame of a blowpipe is ideal for working with small tubes and joints of lead glass. Its hot tip allows for precise heating and re-oxidation of reduced lead.
- A brush flame is useful for heating larger areas of glass and can be modified by adjusting the air and gas supply. A large, highly oxidizing brush flame is essential for working with lead glass without causing discoloration.
- Reduced lead on the surface of lead glass can be re-oxidized by heating it in the oxidising flame. This process is important for preventing discoloration and maintaining the glass’s workability.
- A brick or a block of wood can be used to check radiation and prevent uneven cooling of glass tubes during heating. This technique helps maintain a consistent temperature across the entire working area.
- The use of compressed oxygen instead of air produces a higher-temperature flame suitable for working with hard glass. Oxygen flames are essential for softening hard glass efficiently without devitrification.
- Vitreous silica is less hard than chalcedony but harder than feldspar. This property allows for cutting and breaking silica using regular tools.
- Vitreous silica exhibits low thermal conductivity, making it an excellent insulator. This property is particularly valuable for electrical applications.
- The melting point of vitreous silica is very high, making it suitable for high-temperature applications. It remains plastic over a wide range of temperatures, allowing for extensive manipulation.
- Vitreous silica is optically inactive and highly transparent to ultraviolet radiation. This property makes it ideal for certain optical instruments.
- Vitreous silica is resistant to most acids, except hydrofluoric acid. It is also readily attacked by alkaline solutions.
- Vitreous silica is slightly permeable to hydrogen at high temperatures. This property needs to be considered when using silica for certain gas experiments.
- Platinum wires cannot be directly sealed into vitreous silica because of their different expansion rates. This limitation presents a challenge for electrical applications with silica apparatus.
- Brazil Pebble, a variety of native silica, is preferred for making vitreous silica apparatus. It is more easily prepared and less prone to splintering compared to other forms of quartz.
- A small, but intense, hot spot is essential for efficient softening of vitreous silica. This requires a well-designed oxy-gas burner that concentrates the flame energy.
- Vitreous silica is prone to a white incrustation during working, possibly caused by alkali contamination. Maintaining cleanliness is crucial for preventing this phenomenon and ensuring the material’s integrity.
Statistics:
- The mean coefficient of expansion of vitreous silica is 0.00000059, about one-seventeenth that of platinum. This low expansion makes it ideal for applications requiring high temperature stability.
- Vitreous silica can withstand temperature changes of over 1000° C., making it remarkably resistant to thermal shock. This property simplifies handling during fabrication and use.
- The density of vitreous silica is approximately 2.21. It is very similar to the density of amorphous silica.
- The mean coefficient of expansion of vitreous silica is 0.0000007 between 0° and 1000° C., according to H. le Chatelier. This measurement indicates the material’s remarkable stability at high temperatures.
- Brazil Pebble chips are heated to a yellow-red heat before plunging into cold water to make them non-splintering. This process creates a more workable material for glassblowing.
- A silica rod 1 mm in diameter can be used as the core for making a silica tube, with platinum wires attached at the ends to hold it in place. This technique allows for controlled heating and shaping of the silica.
- A large, roaring oxy-gas flame is not very efficient for working with vitreous silica. A more focused and intense flame, produced by a well-designed burner, is preferable for softening and shaping the material.
Terms:
- Vitreous silica: A highly pure form of silica with unique properties, including high melting point, low thermal expansion, and resistance to thermal shock.
- Devitrification: The process of a glass or silica becoming less transparent and developing a crystalline structure, often caused by contamination or improper heating.
- Annealing: The process of slowly cooling hot glass or silica to relieve internal stresses and prevent cracking.
- Blowpipe: A device that uses a stream of air to direct a flame for heating and shaping glass and silica.
- Brush flame: A wide, non-luminous flame produced by a blowpipe, suitable for heating larger areas of glass.
- Pointed flame: A narrow, focused flame with a hot tip, used for heating small areas of glass and for re-oxidizing reduced lead.
- Oxy-gas flame: A high-temperature flame produced by burning oxygen and a fuel gas like hydrogen, used for working with vitreous silica.
- Brazil Pebble: A variety of native silica, favored for its purity and ease of preparation for working with vitreous silica.
- Quartz fibres: Extremely thin threads of vitreous silica with exceptional strength and elasticity, used in various scientific applications.
Examples:
- Making a thistle funnel: The guide illustrates the process of creating a thistle funnel, highlighting the steps involved in expanding a tube into a bulb, piercing it, and shaping the funnel.
- Closing tubes containing chemicals: The text explains how to securely seal the ends of tubes containing chemicals, ensuring they can withstand high temperatures without leakage.
- Hofman’s Apparatus for electrolysis of water: The guide provides a step-by-step guide for constructing Hofman’s apparatus, which involves joining tubes, attaching taps, and sealing platinum electrodes.
- Making a vacuum tube: The construction of a vacuum tube illustrates the process of combining various parts, including bulbs, electrodes, and tubes, to create a complex apparatus.
- Connecting heavy apparatus: The text describes a method for joining heavy, non-movable equipment using a hand-held blowpipe and controlled pressure to ensure a secure and air-tight seal.
- Mercury joints: Various types of mercury joints are discussed, demonstrating how mercury can be used to create air-tight connections between different pieces of apparatus.
- Vacuum taps: The book explains the functionality of vacuum taps, like Cetti’s and Gimmingham’s, and their use for controlling gas flow and maintaining vacuum in laboratory experiments.
- Air traps: The guide explores different types of air traps, highlighting their function in preventing air bubbles from being introduced into evacuated spaces during mercury flow.
- Calibrating a burette: The text explains the process of calibrating a burette, which involves filling it with water, drawing off portions, and weighing them to determine the exact volume delivered at each division.
- Calibrating a tube for measuring gases: The guide outlines the procedure for calibrating a tube for measuring gas volumes using a known volume of mercury. This process involves filling the tube with mercury, weighing it, and transferring the mercury into the graduated tube to determine its capacity.
Conclusion:
This 1916 manual on glassblowing and vitreous silica serves as a valuable guide for scientists and students looking to acquire essential laboratory skills. The text provides clear and detailed instructions on a wide range of techniques, including essential glassblowing operations, building complex apparatus, and working with the relatively new material, vitreous silica. The guide emphasizes the importance of careful handling, proper annealing, and maintaining cleanliness to achieve optimal results and prevent breakage. The historical context of the text provides insight into the evolving needs of scientific research at the time and the increasing demand for custom-made equipment.