The reason "allmählich" is written with an 'h' is because it is derived from the Middle High German word "allemal," which means "every time" or "always." The 'h' was added to indicate the gradual nature of the action or process. On the other hand, "Mittag" is written with only two 't's because it is a compound word made up of "Mit" (mid) and "Tag" (day), and the double 't' is not necessary for pronunciation or etymological reasons. **

The reason "allmählich" is written with an "h" and "Mittag" with only two "t" is due to the different origins of the words. "Allmählich" is derived from the Middle High German word "allemâlîche," where the "h" was originally present. Over time, the spelling of the word evolved to its current form, retaining the "h." On the other hand, "Mittag" comes from the Middle High German word "mittac," which did not have an extra "t" in its spelling. As the word transitioned into modern German, the extra "t" was not added, resulting in the spelling "Mittag" with only two "t." **

The spelling of "allmählich" with an "h" and "Mittag" with only two "t" is due to the different etymological origins of the two words. "Allmählich" is derived from the Middle High German word "allemâlîch," which evolved from the Old High German "allemalîh," where the "h" was pronounced. On the other hand, "Mittag" comes from the Middle High German word "mittac," which did not have an "h" in its spelling. Over time, the spelling of words can change based on their historical development and pronunciation. **

The reason "allmählich" is written with an 'h' is because it is derived from the Middle High German word "allemâlîche," where the 'h' was present. Over time, the spelling evolved but retained the 'h.' On the other hand, "Mittag" is a compound word made up of "Mit" and "Tag," and in compound words, the double consonant rule does not apply. Therefore, "Mittag" is spelled with only two t's. **

The reason "allmählich" is written with an "h" is because it is derived from the Middle High German word "allemal," which means "every time" or "each time." The "h" was added over time to reflect the pronunciation changes in the German language. On the other hand, "Mittag" is written with only two "t's" because it is a compound word made up of "Mit" (mid) and "Tag" (day), and the double "t" is not necessary to convey the pronunciation of the word. **

The valves on heating pipes are typically ball valves or gate valves. Ball valves have a spherical disc inside that controls the flow of water by rotating the handle, while gate valves have a gate or wedge that moves up and down to control the flow. Both types of valves are used to regulate the flow of hot water through the heating system and can be manually operated to adjust the temperature or shut off the flow completely. **

The 'h' in "allmählich" is present to indicate the pronunciation of the 'ch' sound as a soft 'h' sound. This is a common feature in German to soften the pronunciation of certain consonants. On the other hand, "Mittag" is spelled with only two 't's because the word is derived from the Old High German word "mittitac," where the double 't' was reduced to a single 't' over time in the modern German spelling. **

The reason "allmählich" is written with an 'h' is because it comes from the Middle High German word "allemālīh," where the 'h' was pronounced. Over time, the pronunciation of the 'h' was dropped, but the spelling remained. On the other hand, "Mittag" is written with only two 't' because it follows the standard German spelling rules for compound words. In compound words, the consonant is usually not doubled if it is followed by a vowel. In this case, the 't' in "Mittag" is followed by an 'a,' so it is not doubled. **